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Case Study – Methods, Examples and Guide

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A case study is a research method that involves an in-depth examination and analysis of a particular phenomenon or case, such as an individual, organization, community, event, or situation.

It is a qualitative research approach that aims to provide a detailed and comprehensive understanding of the case being studied. Case studies typically involve multiple sources of data, including interviews, observations, documents, and artifacts, which are analyzed using various techniques, such as content analysis, thematic analysis, and grounded theory. The findings of a case study are often used to develop theories, inform policy or practice, or generate new research questions.

Types of Case Study

Types and Methods of Case Study are as follows:

Single-Case Study

A single-case study is an in-depth analysis of a single case. This type of case study is useful when the researcher wants to understand a specific phenomenon in detail.

For Example , A researcher might conduct a single-case study on a particular individual to understand their experiences with a particular health condition or a specific organization to explore their management practices. The researcher collects data from multiple sources, such as interviews, observations, and documents, and uses various techniques to analyze the data, such as content analysis or thematic analysis. The findings of a single-case study are often used to generate new research questions, develop theories, or inform policy or practice.

Multiple-Case Study

A multiple-case study involves the analysis of several cases that are similar in nature. This type of case study is useful when the researcher wants to identify similarities and differences between the cases.

For Example, a researcher might conduct a multiple-case study on several companies to explore the factors that contribute to their success or failure. The researcher collects data from each case, compares and contrasts the findings, and uses various techniques to analyze the data, such as comparative analysis or pattern-matching. The findings of a multiple-case study can be used to develop theories, inform policy or practice, or generate new research questions.

Exploratory Case Study

An exploratory case study is used to explore a new or understudied phenomenon. This type of case study is useful when the researcher wants to generate hypotheses or theories about the phenomenon.

For Example, a researcher might conduct an exploratory case study on a new technology to understand its potential impact on society. The researcher collects data from multiple sources, such as interviews, observations, and documents, and uses various techniques to analyze the data, such as grounded theory or content analysis. The findings of an exploratory case study can be used to generate new research questions, develop theories, or inform policy or practice.

Descriptive Case Study

A descriptive case study is used to describe a particular phenomenon in detail. This type of case study is useful when the researcher wants to provide a comprehensive account of the phenomenon.

For Example, a researcher might conduct a descriptive case study on a particular community to understand its social and economic characteristics. The researcher collects data from multiple sources, such as interviews, observations, and documents, and uses various techniques to analyze the data, such as content analysis or thematic analysis. The findings of a descriptive case study can be used to inform policy or practice or generate new research questions.

Instrumental Case Study

An instrumental case study is used to understand a particular phenomenon that is instrumental in achieving a particular goal. This type of case study is useful when the researcher wants to understand the role of the phenomenon in achieving the goal.

For Example, a researcher might conduct an instrumental case study on a particular policy to understand its impact on achieving a particular goal, such as reducing poverty. The researcher collects data from multiple sources, such as interviews, observations, and documents, and uses various techniques to analyze the data, such as content analysis or thematic analysis. The findings of an instrumental case study can be used to inform policy or practice or generate new research questions.

Case Study Data Collection Methods

Here are some common data collection methods for case studies:

Interviews involve asking questions to individuals who have knowledge or experience relevant to the case study. Interviews can be structured (where the same questions are asked to all participants) or unstructured (where the interviewer follows up on the responses with further questions). Interviews can be conducted in person, over the phone, or through video conferencing.

Observations

Observations involve watching and recording the behavior and activities of individuals or groups relevant to the case study. Observations can be participant (where the researcher actively participates in the activities) or non-participant (where the researcher observes from a distance). Observations can be recorded using notes, audio or video recordings, or photographs.

Documents can be used as a source of information for case studies. Documents can include reports, memos, emails, letters, and other written materials related to the case study. Documents can be collected from the case study participants or from public sources.

Surveys involve asking a set of questions to a sample of individuals relevant to the case study. Surveys can be administered in person, over the phone, through mail or email, or online. Surveys can be used to gather information on attitudes, opinions, or behaviors related to the case study.

Artifacts are physical objects relevant to the case study. Artifacts can include tools, equipment, products, or other objects that provide insights into the case study phenomenon.

How to conduct Case Study Research

Conducting a case study research involves several steps that need to be followed to ensure the quality and rigor of the study. Here are the steps to conduct case study research:

• Define the research questions: The first step in conducting a case study research is to define the research questions. The research questions should be specific, measurable, and relevant to the case study phenomenon under investigation.
• Select the case: The next step is to select the case or cases to be studied. The case should be relevant to the research questions and should provide rich and diverse data that can be used to answer the research questions.
• Collect data: Data can be collected using various methods, such as interviews, observations, documents, surveys, and artifacts. The data collection method should be selected based on the research questions and the nature of the case study phenomenon.
• Analyze the data: The data collected from the case study should be analyzed using various techniques, such as content analysis, thematic analysis, or grounded theory. The analysis should be guided by the research questions and should aim to provide insights and conclusions relevant to the research questions.
• Draw conclusions: The conclusions drawn from the case study should be based on the data analysis and should be relevant to the research questions. The conclusions should be supported by evidence and should be clearly stated.
• Validate the findings: The findings of the case study should be validated by reviewing the data and the analysis with participants or other experts in the field. This helps to ensure the validity and reliability of the findings.
• Write the report: The final step is to write the report of the case study research. The report should provide a clear description of the case study phenomenon, the research questions, the data collection methods, the data analysis, the findings, and the conclusions. The report should be written in a clear and concise manner and should follow the guidelines for academic writing.

Examples of Case Study

Here are some examples of case study research:

• The Hawthorne Studies : Conducted between 1924 and 1932, the Hawthorne Studies were a series of case studies conducted by Elton Mayo and his colleagues to examine the impact of work environment on employee productivity. The studies were conducted at the Hawthorne Works plant of the Western Electric Company in Chicago and included interviews, observations, and experiments.
• The Stanford Prison Experiment: Conducted in 1971, the Stanford Prison Experiment was a case study conducted by Philip Zimbardo to examine the psychological effects of power and authority. The study involved simulating a prison environment and assigning participants to the role of guards or prisoners. The study was controversial due to the ethical issues it raised.
• The Challenger Disaster: The Challenger Disaster was a case study conducted to examine the causes of the Space Shuttle Challenger explosion in 1986. The study included interviews, observations, and analysis of data to identify the technical, organizational, and cultural factors that contributed to the disaster.
• The Enron Scandal: The Enron Scandal was a case study conducted to examine the causes of the Enron Corporation’s bankruptcy in 2001. The study included interviews, analysis of financial data, and review of documents to identify the accounting practices, corporate culture, and ethical issues that led to the company’s downfall.
• The Fukushima Nuclear Disaster : The Fukushima Nuclear Disaster was a case study conducted to examine the causes of the nuclear accident that occurred at the Fukushima Daiichi Nuclear Power Plant in Japan in 2011. The study included interviews, analysis of data, and review of documents to identify the technical, organizational, and cultural factors that contributed to the disaster.

Application of Case Study

Case studies have a wide range of applications across various fields and industries. Here are some examples:

Business and Management

Case studies are widely used in business and management to examine real-life situations and develop problem-solving skills. Case studies can help students and professionals to develop a deep understanding of business concepts, theories, and best practices.

Case studies are used in healthcare to examine patient care, treatment options, and outcomes. Case studies can help healthcare professionals to develop critical thinking skills, diagnose complex medical conditions, and develop effective treatment plans.

Case studies are used in education to examine teaching and learning practices. Case studies can help educators to develop effective teaching strategies, evaluate student progress, and identify areas for improvement.

Social Sciences

Case studies are widely used in social sciences to examine human behavior, social phenomena, and cultural practices. Case studies can help researchers to develop theories, test hypotheses, and gain insights into complex social issues.

Law and Ethics

Case studies are used in law and ethics to examine legal and ethical dilemmas. Case studies can help lawyers, policymakers, and ethical professionals to develop critical thinking skills, analyze complex cases, and make informed decisions.

Purpose of Case Study

The purpose of a case study is to provide a detailed analysis of a specific phenomenon, issue, or problem in its real-life context. A case study is a qualitative research method that involves the in-depth exploration and analysis of a particular case, which can be an individual, group, organization, event, or community.

The primary purpose of a case study is to generate a comprehensive and nuanced understanding of the case, including its history, context, and dynamics. Case studies can help researchers to identify and examine the underlying factors, processes, and mechanisms that contribute to the case and its outcomes. This can help to develop a more accurate and detailed understanding of the case, which can inform future research, practice, or policy.

Case studies can also serve other purposes, including:

• Illustrating a theory or concept: Case studies can be used to illustrate and explain theoretical concepts and frameworks, providing concrete examples of how they can be applied in real-life situations.
• Developing hypotheses: Case studies can help to generate hypotheses about the causal relationships between different factors and outcomes, which can be tested through further research.
• Providing insight into complex issues: Case studies can provide insights into complex and multifaceted issues, which may be difficult to understand through other research methods.
• Informing practice or policy: Case studies can be used to inform practice or policy by identifying best practices, lessons learned, or areas for improvement.

Advantages of Case Study Research

There are several advantages of case study research, including:

• In-depth exploration: Case study research allows for a detailed exploration and analysis of a specific phenomenon, issue, or problem in its real-life context. This can provide a comprehensive understanding of the case and its dynamics, which may not be possible through other research methods.
• Rich data: Case study research can generate rich and detailed data, including qualitative data such as interviews, observations, and documents. This can provide a nuanced understanding of the case and its complexity.
• Holistic perspective: Case study research allows for a holistic perspective of the case, taking into account the various factors, processes, and mechanisms that contribute to the case and its outcomes. This can help to develop a more accurate and comprehensive understanding of the case.
• Theory development: Case study research can help to develop and refine theories and concepts by providing empirical evidence and concrete examples of how they can be applied in real-life situations.
• Practical application: Case study research can inform practice or policy by identifying best practices, lessons learned, or areas for improvement.
• Contextualization: Case study research takes into account the specific context in which the case is situated, which can help to understand how the case is influenced by the social, cultural, and historical factors of its environment.

Limitations of Case Study Research

There are several limitations of case study research, including:

• Limited generalizability : Case studies are typically focused on a single case or a small number of cases, which limits the generalizability of the findings. The unique characteristics of the case may not be applicable to other contexts or populations, which may limit the external validity of the research.
• Biased sampling: Case studies may rely on purposive or convenience sampling, which can introduce bias into the sample selection process. This may limit the representativeness of the sample and the generalizability of the findings.
• Subjectivity: Case studies rely on the interpretation of the researcher, which can introduce subjectivity into the analysis. The researcher’s own biases, assumptions, and perspectives may influence the findings, which may limit the objectivity of the research.
• Limited control: Case studies are typically conducted in naturalistic settings, which limits the control that the researcher has over the environment and the variables being studied. This may limit the ability to establish causal relationships between variables.
• Time-consuming: Case studies can be time-consuming to conduct, as they typically involve a detailed exploration and analysis of a specific case. This may limit the feasibility of conducting multiple case studies or conducting case studies in a timely manner.
• Resource-intensive: Case studies may require significant resources, including time, funding, and expertise. This may limit the ability of researchers to conduct case studies in resource-constrained settings.

About the author

Muhammad Hassan

Researcher, Academic Writer, Web developer

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Methodology

• What Is a Case Study? | Definition, Examples & Methods

What Is a Case Study? | Definition, Examples & Methods

Published on May 8, 2019 by Shona McCombes . Revised on November 20, 2023.

A case study is a detailed study of a specific subject, such as a person, group, place, event, organization, or phenomenon. Case studies are commonly used in social, educational, clinical, and business research.

A case study research design usually involves qualitative methods , but quantitative methods are sometimes also used. Case studies are good for describing , comparing, evaluating and understanding different aspects of a research problem .

Table of contents

When to do a case study, step 1: select a case, step 2: build a theoretical framework, step 3: collect your data, step 4: describe and analyze the case, other interesting articles.

A case study is an appropriate research design when you want to gain concrete, contextual, in-depth knowledge about a specific real-world subject. It allows you to explore the key characteristics, meanings, and implications of the case.

Case studies are often a good choice in a thesis or dissertation . They keep your project focused and manageable when you don’t have the time or resources to do large-scale research.

You might use just one complex case study where you explore a single subject in depth, or conduct multiple case studies to compare and illuminate different aspects of your research problem.

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Once you have developed your problem statement and research questions , you should be ready to choose the specific case that you want to focus on. A good case study should have the potential to:

• Provide new or unexpected insights into the subject
• Challenge or complicate existing assumptions and theories
• Propose practical courses of action to resolve a problem
• Open up new directions for future research

TipIf your research is more practical in nature and aims to simultaneously investigate an issue as you solve it, consider conducting action research instead.

Unlike quantitative or experimental research , a strong case study does not require a random or representative sample. In fact, case studies often deliberately focus on unusual, neglected, or outlying cases which may shed new light on the research problem.

Example of an outlying case studyIn the 1960s the town of Roseto, Pennsylvania was discovered to have extremely low rates of heart disease compared to the US average. It became an important case study for understanding previously neglected causes of heart disease.

However, you can also choose a more common or representative case to exemplify a particular category, experience or phenomenon.

Example of a representative case studyIn the 1920s, two sociologists used Muncie, Indiana as a case study of a typical American city that supposedly exemplified the changing culture of the US at the time.

While case studies focus more on concrete details than general theories, they should usually have some connection with theory in the field. This way the case study is not just an isolated description, but is integrated into existing knowledge about the topic. It might aim to:

• Exemplify a theory by showing how it explains the case under investigation
• Expand on a theory by uncovering new concepts and ideas that need to be incorporated
• Challenge a theory by exploring an outlier case that doesn’t fit with established assumptions

To ensure that your analysis of the case has a solid academic grounding, you should conduct a literature review of sources related to the topic and develop a theoretical framework . This means identifying key concepts and theories to guide your analysis and interpretation.

There are many different research methods you can use to collect data on your subject. Case studies tend to focus on qualitative data using methods such as interviews , observations , and analysis of primary and secondary sources (e.g., newspaper articles, photographs, official records). Sometimes a case study will also collect quantitative data.

Example of a mixed methods case studyFor a case study of a wind farm development in a rural area, you could collect quantitative data on employment rates and business revenue, collect qualitative data on local people’s perceptions and experiences, and analyze local and national media coverage of the development.

The aim is to gain as thorough an understanding as possible of the case and its context.

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In writing up the case study, you need to bring together all the relevant aspects to give as complete a picture as possible of the subject.

How you report your findings depends on the type of research you are doing. Some case studies are structured like a standard scientific paper or thesis , with separate sections or chapters for the methods , results and discussion .

Others are written in a more narrative style, aiming to explore the case from various angles and analyze its meanings and implications (for example, by using textual analysis or discourse analysis ).

In all cases, though, make sure to give contextual details about the case, connect it back to the literature and theory, and discuss how it fits into wider patterns or debates.

If you want to know more about statistics , methodology , or research bias , make sure to check out some of our other articles with explanations and examples.

• Normal distribution
• Degrees of freedom
• Null hypothesis
• Discourse analysis
• Control groups
• Mixed methods research
• Non-probability sampling
• Quantitative research
• Ecological validity

Research bias

• Rosenthal effect
• Implicit bias
• Cognitive bias
• Selection bias
• Negativity bias
• Status quo bias

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Organizing Your Social Sciences Research Assignments

• Annotated Bibliography
• Analyzing a Scholarly Journal Article
• Group Presentations
• Dealing with Nervousness
• Using Visual Aids
• Grading Someone Else's Paper
• Types of Structured Group Activities
• Group Project Survival Skills
• Leading a Class Discussion
• Multiple Book Review Essay
• Reviewing Collected Works
• Writing a Case Analysis Paper
• Writing a Case Study
• About Informed Consent
• Writing Field Notes
• Writing a Policy Memo
• Writing a Reflective Paper
• Writing a Research Proposal
• Generative AI and Writing
• Acknowledgments

A case study research paper examines a person, place, event, condition, phenomenon, or other type of subject of analysis in order to extrapolate  key themes and results that help predict future trends, illuminate previously hidden issues that can be applied to practice, and/or provide a means for understanding an important research problem with greater clarity. A case study research paper usually examines a single subject of analysis, but case study papers can also be designed as a comparative investigation that shows relationships between two or more subjects. The methods used to study a case can rest within a quantitative, qualitative, or mixed-method investigative paradigm.

Case Studies. Writing@CSU. Colorado State University; Mills, Albert J. , Gabrielle Durepos, and Eiden Wiebe, editors. Encyclopedia of Case Study Research . Thousand Oaks, CA: SAGE Publications, 2010 ; “What is a Case Study?” In Swanborn, Peter G. Case Study Research: What, Why and How? London: SAGE, 2010.

How to Approach Writing a Case Study Research Paper

General information about how to choose a topic to investigate can be found under the " Choosing a Research Problem " tab in the Organizing Your Social Sciences Research Paper writing guide. Review this page because it may help you identify a subject of analysis that can be investigated using a case study design.

However, identifying a case to investigate involves more than choosing the research problem . A case study encompasses a problem contextualized around the application of in-depth analysis, interpretation, and discussion, often resulting in specific recommendations for action or for improving existing conditions. As Seawright and Gerring note, practical considerations such as time and access to information can influence case selection, but these issues should not be the sole factors used in describing the methodological justification for identifying a particular case to study. Given this, selecting a case includes considering the following:

• The case represents an unusual or atypical example of a research problem that requires more in-depth analysis? Cases often represent a topic that rests on the fringes of prior investigations because the case may provide new ways of understanding the research problem. For example, if the research problem is to identify strategies to improve policies that support girl's access to secondary education in predominantly Muslim nations, you could consider using Azerbaijan as a case study rather than selecting a more obvious nation in the Middle East. Doing so may reveal important new insights into recommending how governments in other predominantly Muslim nations can formulate policies that support improved access to education for girls.
• The case provides important insight or illuminate a previously hidden problem? In-depth analysis of a case can be based on the hypothesis that the case study will reveal trends or issues that have not been exposed in prior research or will reveal new and important implications for practice. For example, anecdotal evidence may suggest drug use among homeless veterans is related to their patterns of travel throughout the day. Assuming prior studies have not looked at individual travel choices as a way to study access to illicit drug use, a case study that observes a homeless veteran could reveal how issues of personal mobility choices facilitate regular access to illicit drugs. Note that it is important to conduct a thorough literature review to ensure that your assumption about the need to reveal new insights or previously hidden problems is valid and evidence-based.
• The case challenges and offers a counter-point to prevailing assumptions? Over time, research on any given topic can fall into a trap of developing assumptions based on outdated studies that are still applied to new or changing conditions or the idea that something should simply be accepted as "common sense," even though the issue has not been thoroughly tested in current practice. A case study analysis may offer an opportunity to gather evidence that challenges prevailing assumptions about a research problem and provide a new set of recommendations applied to practice that have not been tested previously. For example, perhaps there has been a long practice among scholars to apply a particular theory in explaining the relationship between two subjects of analysis. Your case could challenge this assumption by applying an innovative theoretical framework [perhaps borrowed from another discipline] to explore whether this approach offers new ways of understanding the research problem. Taking a contrarian stance is one of the most important ways that new knowledge and understanding develops from existing literature.
• The case provides an opportunity to pursue action leading to the resolution of a problem? Another way to think about choosing a case to study is to consider how the results from investigating a particular case may result in findings that reveal ways in which to resolve an existing or emerging problem. For example, studying the case of an unforeseen incident, such as a fatal accident at a railroad crossing, can reveal hidden issues that could be applied to preventative measures that contribute to reducing the chance of accidents in the future. In this example, a case study investigating the accident could lead to a better understanding of where to strategically locate additional signals at other railroad crossings so as to better warn drivers of an approaching train, particularly when visibility is hindered by heavy rain, fog, or at night.
• The case offers a new direction in future research? A case study can be used as a tool for an exploratory investigation that highlights the need for further research about the problem. A case can be used when there are few studies that help predict an outcome or that establish a clear understanding about how best to proceed in addressing a problem. For example, after conducting a thorough literature review [very important!], you discover that little research exists showing the ways in which women contribute to promoting water conservation in rural communities of east central Africa. A case study of how women contribute to saving water in a rural village of Uganda can lay the foundation for understanding the need for more thorough research that documents how women in their roles as cooks and family caregivers think about water as a valuable resource within their community. This example of a case study could also point to the need for scholars to build new theoretical frameworks around the topic [e.g., applying feminist theories of work and family to the issue of water conservation].

Eisenhardt, Kathleen M. “Building Theories from Case Study Research.” Academy of Management Review 14 (October 1989): 532-550; Emmel, Nick. Sampling and Choosing Cases in Qualitative Research: A Realist Approach . Thousand Oaks, CA: SAGE Publications, 2013; Gerring, John. “What Is a Case Study and What Is It Good for?” American Political Science Review 98 (May 2004): 341-354; Mills, Albert J. , Gabrielle Durepos, and Eiden Wiebe, editors. Encyclopedia of Case Study Research . Thousand Oaks, CA: SAGE Publications, 2010; Seawright, Jason and John Gerring. "Case Selection Techniques in Case Study Research." Political Research Quarterly 61 (June 2008): 294-308.

Structure and Writing Style

The purpose of a paper in the social sciences designed around a case study is to thoroughly investigate a subject of analysis in order to reveal a new understanding about the research problem and, in so doing, contributing new knowledge to what is already known from previous studies. In applied social sciences disciplines [e.g., education, social work, public administration, etc.], case studies may also be used to reveal best practices, highlight key programs, or investigate interesting aspects of professional work.

In general, the structure of a case study research paper is not all that different from a standard college-level research paper. However, there are subtle differences you should be aware of. Here are the key elements to organizing and writing a case study research paper.

I.  Introduction

As with any research paper, your introduction should serve as a roadmap for your readers to ascertain the scope and purpose of your study . The introduction to a case study research paper, however, should not only describe the research problem and its significance, but you should also succinctly describe why the case is being used and how it relates to addressing the problem. The two elements should be linked. With this in mind, a good introduction answers these four questions:

• What is being studied? Describe the research problem and describe the subject of analysis [the case] you have chosen to address the problem. Explain how they are linked and what elements of the case will help to expand knowledge and understanding about the problem.
• Why is this topic important to investigate? Describe the significance of the research problem and state why a case study design and the subject of analysis that the paper is designed around is appropriate in addressing the problem.
• What did we know about this topic before I did this study? Provide background that helps lead the reader into the more in-depth literature review to follow. If applicable, summarize prior case study research applied to the research problem and why it fails to adequately address the problem. Describe why your case will be useful. If no prior case studies have been used to address the research problem, explain why you have selected this subject of analysis.
• How will this study advance new knowledge or new ways of understanding? Explain why your case study will be suitable in helping to expand knowledge and understanding about the research problem.

Each of these questions should be addressed in no more than a few paragraphs. Exceptions to this can be when you are addressing a complex research problem or subject of analysis that requires more in-depth background information.

II.  Literature Review

The literature review for a case study research paper is generally structured the same as it is for any college-level research paper. The difference, however, is that the literature review is focused on providing background information and  enabling historical interpretation of the subject of analysis in relation to the research problem the case is intended to address . This includes synthesizing studies that help to:

• Place relevant works in the context of their contribution to understanding the case study being investigated . This would involve summarizing studies that have used a similar subject of analysis to investigate the research problem. If there is literature using the same or a very similar case to study, you need to explain why duplicating past research is important [e.g., conditions have changed; prior studies were conducted long ago, etc.].
• Describe the relationship each work has to the others under consideration that informs the reader why this case is applicable . Your literature review should include a description of any works that support using the case to investigate the research problem and the underlying research questions.
• Identify new ways to interpret prior research using the case study . If applicable, review any research that has examined the research problem using a different research design. Explain how your use of a case study design may reveal new knowledge or a new perspective or that can redirect research in an important new direction.
• Resolve conflicts amongst seemingly contradictory previous studies . This refers to synthesizing any literature that points to unresolved issues of concern about the research problem and describing how the subject of analysis that forms the case study can help resolve these existing contradictions.
• Point the way in fulfilling a need for additional research . Your review should examine any literature that lays a foundation for understanding why your case study design and the subject of analysis around which you have designed your study may reveal a new way of approaching the research problem or offer a perspective that points to the need for additional research.
• Expose any gaps that exist in the literature that the case study could help to fill . Summarize any literature that not only shows how your subject of analysis contributes to understanding the research problem, but how your case contributes to a new way of understanding the problem that prior research has failed to do.
• Locate your own research within the context of existing literature [very important!] . Collectively, your literature review should always place your case study within the larger domain of prior research about the problem. The overarching purpose of reviewing pertinent literature in a case study paper is to demonstrate that you have thoroughly identified and synthesized prior studies in relation to explaining the relevance of the case in addressing the research problem.

III.  Method

In this section, you explain why you selected a particular case [i.e., subject of analysis] and the strategy you used to identify and ultimately decide that your case was appropriate in addressing the research problem. The way you describe the methods used varies depending on the type of subject of analysis that constitutes your case study.

If your subject of analysis is an incident or event . In the social and behavioral sciences, the event or incident that represents the case to be studied is usually bounded by time and place, with a clear beginning and end and with an identifiable location or position relative to its surroundings. The subject of analysis can be a rare or critical event or it can focus on a typical or regular event. The purpose of studying a rare event is to illuminate new ways of thinking about the broader research problem or to test a hypothesis. Critical incident case studies must describe the method by which you identified the event and explain the process by which you determined the validity of this case to inform broader perspectives about the research problem or to reveal new findings. However, the event does not have to be a rare or uniquely significant to support new thinking about the research problem or to challenge an existing hypothesis. For example, Walo, Bull, and Breen conducted a case study to identify and evaluate the direct and indirect economic benefits and costs of a local sports event in the City of Lismore, New South Wales, Australia. The purpose of their study was to provide new insights from measuring the impact of a typical local sports event that prior studies could not measure well because they focused on large "mega-events." Whether the event is rare or not, the methods section should include an explanation of the following characteristics of the event: a) when did it take place; b) what were the underlying circumstances leading to the event; and, c) what were the consequences of the event in relation to the research problem.

If your subject of analysis is a person. Explain why you selected this particular individual to be studied and describe what experiences they have had that provide an opportunity to advance new understandings about the research problem. Mention any background about this person which might help the reader understand the significance of their experiences that make them worthy of study. This includes describing the relationships this person has had with other people, institutions, and/or events that support using them as the subject for a case study research paper. It is particularly important to differentiate the person as the subject of analysis from others and to succinctly explain how the person relates to examining the research problem [e.g., why is one politician in a particular local election used to show an increase in voter turnout from any other candidate running in the election]. Note that these issues apply to a specific group of people used as a case study unit of analysis [e.g., a classroom of students].

If your subject of analysis is a place. In general, a case study that investigates a place suggests a subject of analysis that is unique or special in some way and that this uniqueness can be used to build new understanding or knowledge about the research problem. A case study of a place must not only describe its various attributes relevant to the research problem [e.g., physical, social, historical, cultural, economic, political], but you must state the method by which you determined that this place will illuminate new understandings about the research problem. It is also important to articulate why a particular place as the case for study is being used if similar places also exist [i.e., if you are studying patterns of homeless encampments of veterans in open spaces, explain why you are studying Echo Park in Los Angeles rather than Griffith Park?]. If applicable, describe what type of human activity involving this place makes it a good choice to study [e.g., prior research suggests Echo Park has more homeless veterans].

If your subject of analysis is a phenomenon. A phenomenon refers to a fact, occurrence, or circumstance that can be studied or observed but with the cause or explanation to be in question. In this sense, a phenomenon that forms your subject of analysis can encompass anything that can be observed or presumed to exist but is not fully understood. In the social and behavioral sciences, the case usually focuses on human interaction within a complex physical, social, economic, cultural, or political system. For example, the phenomenon could be the observation that many vehicles used by ISIS fighters are small trucks with English language advertisements on them. The research problem could be that ISIS fighters are difficult to combat because they are highly mobile. The research questions could be how and by what means are these vehicles used by ISIS being supplied to the militants and how might supply lines to these vehicles be cut off? How might knowing the suppliers of these trucks reveal larger networks of collaborators and financial support? A case study of a phenomenon most often encompasses an in-depth analysis of a cause and effect that is grounded in an interactive relationship between people and their environment in some way.

NOTE:   The choice of the case or set of cases to study cannot appear random. Evidence that supports the method by which you identified and chose your subject of analysis should clearly support investigation of the research problem and linked to key findings from your literature review. Be sure to cite any studies that helped you determine that the case you chose was appropriate for examining the problem.

IV.  Discussion

The main elements of your discussion section are generally the same as any research paper, but centered around interpreting and drawing conclusions about the key findings from your analysis of the case study. Note that a general social sciences research paper may contain a separate section to report findings. However, in a paper designed around a case study, it is common to combine a description of the results with the discussion about their implications. The objectives of your discussion section should include the following:

Reiterate the Research Problem/State the Major Findings Briefly reiterate the research problem you are investigating and explain why the subject of analysis around which you designed the case study were used. You should then describe the findings revealed from your study of the case using direct, declarative, and succinct proclamation of the study results. Highlight any findings that were unexpected or especially profound.

Explain the Meaning of the Findings and Why They are Important Systematically explain the meaning of your case study findings and why you believe they are important. Begin this part of the section by repeating what you consider to be your most important or surprising finding first, then systematically review each finding. Be sure to thoroughly extrapolate what your analysis of the case can tell the reader about situations or conditions beyond the actual case that was studied while, at the same time, being careful not to misconstrue or conflate a finding that undermines the external validity of your conclusions.

Relate the Findings to Similar Studies No study in the social sciences is so novel or possesses such a restricted focus that it has absolutely no relation to previously published research. The discussion section should relate your case study results to those found in other studies, particularly if questions raised from prior studies served as the motivation for choosing your subject of analysis. This is important because comparing and contrasting the findings of other studies helps support the overall importance of your results and it highlights how and in what ways your case study design and the subject of analysis differs from prior research about the topic.

Consider Alternative Explanations of the Findings Remember that the purpose of social science research is to discover and not to prove. When writing the discussion section, you should carefully consider all possible explanations revealed by the case study results, rather than just those that fit your hypothesis or prior assumptions and biases. Be alert to what the in-depth analysis of the case may reveal about the research problem, including offering a contrarian perspective to what scholars have stated in prior research if that is how the findings can be interpreted from your case.

Acknowledge the Study's Limitations You can state the study's limitations in the conclusion section of your paper but describing the limitations of your subject of analysis in the discussion section provides an opportunity to identify the limitations and explain why they are not significant. This part of the discussion section should also note any unanswered questions or issues your case study could not address. More detailed information about how to document any limitations to your research can be found here .

Suggest Areas for Further Research Although your case study may offer important insights about the research problem, there are likely additional questions related to the problem that remain unanswered or findings that unexpectedly revealed themselves as a result of your in-depth analysis of the case. Be sure that the recommendations for further research are linked to the research problem and that you explain why your recommendations are valid in other contexts and based on the original assumptions of your study.

V.  Conclusion

As with any research paper, you should summarize your conclusion in clear, simple language; emphasize how the findings from your case study differs from or supports prior research and why. Do not simply reiterate the discussion section. Provide a synthesis of key findings presented in the paper to show how these converge to address the research problem. If you haven't already done so in the discussion section, be sure to document the limitations of your case study and any need for further research.

The function of your paper's conclusion is to: 1) reiterate the main argument supported by the findings from your case study; 2) state clearly the context, background, and necessity of pursuing the research problem using a case study design in relation to an issue, controversy, or a gap found from reviewing the literature; and, 3) provide a place to persuasively and succinctly restate the significance of your research problem, given that the reader has now been presented with in-depth information about the topic.

Consider the following points to help ensure your conclusion is appropriate:

• If the argument or purpose of your paper is complex, you may need to summarize these points for your reader.
• If prior to your conclusion, you have not yet explained the significance of your findings or if you are proceeding inductively, use the conclusion of your paper to describe your main points and explain their significance.
• Move from a detailed to a general level of consideration of the case study's findings that returns the topic to the context provided by the introduction or within a new context that emerges from your case study findings.

Note that, depending on the discipline you are writing in or the preferences of your professor, the concluding paragraph may contain your final reflections on the evidence presented as it applies to practice or on the essay's central research problem. However, the nature of being introspective about the subject of analysis you have investigated will depend on whether you are explicitly asked to express your observations in this way.

Problems to Avoid

Overgeneralization One of the goals of a case study is to lay a foundation for understanding broader trends and issues applied to similar circumstances. However, be careful when drawing conclusions from your case study. They must be evidence-based and grounded in the results of the study; otherwise, it is merely speculation. Looking at a prior example, it would be incorrect to state that a factor in improving girls access to education in Azerbaijan and the policy implications this may have for improving access in other Muslim nations is due to girls access to social media if there is no documentary evidence from your case study to indicate this. There may be anecdotal evidence that retention rates were better for girls who were engaged with social media, but this observation would only point to the need for further research and would not be a definitive finding if this was not a part of your original research agenda.

Failure to Document Limitations No case is going to reveal all that needs to be understood about a research problem. Therefore, just as you have to clearly state the limitations of a general research study , you must describe the specific limitations inherent in the subject of analysis. For example, the case of studying how women conceptualize the need for water conservation in a village in Uganda could have limited application in other cultural contexts or in areas where fresh water from rivers or lakes is plentiful and, therefore, conservation is understood more in terms of managing access rather than preserving access to a scarce resource.

Failure to Extrapolate All Possible Implications Just as you don't want to over-generalize from your case study findings, you also have to be thorough in the consideration of all possible outcomes or recommendations derived from your findings. If you do not, your reader may question the validity of your analysis, particularly if you failed to document an obvious outcome from your case study research. For example, in the case of studying the accident at the railroad crossing to evaluate where and what types of warning signals should be located, you failed to take into consideration speed limit signage as well as warning signals. When designing your case study, be sure you have thoroughly addressed all aspects of the problem and do not leave gaps in your analysis that leave the reader questioning the results.

Case Studies. Writing@CSU. Colorado State University; Gerring, John. Case Study Research: Principles and Practices . New York: Cambridge University Press, 2007; Merriam, Sharan B. Qualitative Research and Case Study Applications in Education . Rev. ed. San Francisco, CA: Jossey-Bass, 1998; Miller, Lisa L. “The Use of Case Studies in Law and Social Science Research.” Annual Review of Law and Social Science 14 (2018): TBD; Mills, Albert J., Gabrielle Durepos, and Eiden Wiebe, editors. Encyclopedia of Case Study Research . Thousand Oaks, CA: SAGE Publications, 2010; Putney, LeAnn Grogan. "Case Study." In Encyclopedia of Research Design , Neil J. Salkind, editor. (Thousand Oaks, CA: SAGE Publications, 2010), pp. 116-120; Simons, Helen. Case Study Research in Practice . London: SAGE Publications, 2009;  Kratochwill,  Thomas R. and Joel R. Levin, editors. Single-Case Research Design and Analysis: New Development for Psychology and Education .  Hilldsale, NJ: Lawrence Erlbaum Associates, 1992; Swanborn, Peter G. Case Study Research: What, Why and How? London : SAGE, 2010; Yin, Robert K. Case Study Research: Design and Methods . 6th edition. Los Angeles, CA, SAGE Publications, 2014; Walo, Maree, Adrian Bull, and Helen Breen. “Achieving Economic Benefits at Local Events: A Case Study of a Local Sports Event.” Festival Management and Event Tourism 4 (1996): 95-106.

Writing Tip

At Least Five Misconceptions about Case Study Research

Social science case studies are often perceived as limited in their ability to create new knowledge because they are not randomly selected and findings cannot be generalized to larger populations. Flyvbjerg examines five misunderstandings about case study research and systematically "corrects" each one. To quote, these are:

Misunderstanding 1 :  General, theoretical [context-independent] knowledge is more valuable than concrete, practical [context-dependent] knowledge. Misunderstanding 2 :  One cannot generalize on the basis of an individual case; therefore, the case study cannot contribute to scientific development. Misunderstanding 3 :  The case study is most useful for generating hypotheses; that is, in the first stage of a total research process, whereas other methods are more suitable for hypotheses testing and theory building. Misunderstanding 4 :  The case study contains a bias toward verification, that is, a tendency to confirm the researcher’s preconceived notions. Misunderstanding 5 :  It is often difficult to summarize and develop general propositions and theories on the basis of specific case studies [p. 221].

While writing your paper, think introspectively about how you addressed these misconceptions because to do so can help you strengthen the validity and reliability of your research by clarifying issues of case selection, the testing and challenging of existing assumptions, the interpretation of key findings, and the summation of case outcomes. Think of a case study research paper as a complete, in-depth narrative about the specific properties and key characteristics of your subject of analysis applied to the research problem.

Flyvbjerg, Bent. “Five Misunderstandings About Case-Study Research.” Qualitative Inquiry 12 (April 2006): 219-245.

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The Ultimate Guide to Qualitative Research - Part 1: The Basics

• Introduction and overview
• What is qualitative research?
• What is qualitative data?
• Examples of qualitative data
• Qualitative vs. quantitative research
• Mixed methods
• Qualitative research preparation
• Theoretical perspective
• Theoretical framework
• Literature reviews

Research question

• Conceptual framework
• Conceptual vs. theoretical framework

Data collection

• Qualitative research methods
• Focus groups
• Observational research

What is a case study?

Applications for case study research, what is a good case study, process of case study design, benefits and limitations of case studies.

• Ethnographical research
• Ethical considerations
• Confidentiality and privacy
• Power dynamics
• Reflexivity

Case studies

Case studies are essential to qualitative research , offering a lens through which researchers can investigate complex phenomena within their real-life contexts. This chapter explores the concept, purpose, applications, examples, and types of case studies and provides guidance on how to conduct case study research effectively.

Whereas quantitative methods look at phenomena at scale, case study research looks at a concept or phenomenon in considerable detail. While analyzing a single case can help understand one perspective regarding the object of research inquiry, analyzing multiple cases can help obtain a more holistic sense of the topic or issue. Let's provide a basic definition of a case study, then explore its characteristics and role in the qualitative research process.

Definition of a case study

A case study in qualitative research is a strategy of inquiry that involves an in-depth investigation of a phenomenon within its real-world context. It provides researchers with the opportunity to acquire an in-depth understanding of intricate details that might not be as apparent or accessible through other methods of research. The specific case or cases being studied can be a single person, group, or organization – demarcating what constitutes a relevant case worth studying depends on the researcher and their research question .

Among qualitative research methods , a case study relies on multiple sources of evidence, such as documents, artifacts, interviews , or observations , to present a complete and nuanced understanding of the phenomenon under investigation. The objective is to illuminate the readers' understanding of the phenomenon beyond its abstract statistical or theoretical explanations.

Characteristics of case studies

Case studies typically possess a number of distinct characteristics that set them apart from other research methods. These characteristics include a focus on holistic description and explanation, flexibility in the design and data collection methods, reliance on multiple sources of evidence, and emphasis on the context in which the phenomenon occurs.

Furthermore, case studies can often involve a longitudinal examination of the case, meaning they study the case over a period of time. These characteristics allow case studies to yield comprehensive, in-depth, and richly contextualized insights about the phenomenon of interest.

The role of case studies in research

Case studies hold a unique position in the broader landscape of research methods aimed at theory development. They are instrumental when the primary research interest is to gain an intensive, detailed understanding of a phenomenon in its real-life context.

In addition, case studies can serve different purposes within research - they can be used for exploratory, descriptive, or explanatory purposes, depending on the research question and objectives. This flexibility and depth make case studies a valuable tool in the toolkit of qualitative researchers.

Remember, a well-conducted case study can offer a rich, insightful contribution to both academic and practical knowledge through theory development or theory verification, thus enhancing our understanding of complex phenomena in their real-world contexts.

What is the purpose of a case study?

Case study research aims for a more comprehensive understanding of phenomena, requiring various research methods to gather information for qualitative analysis . Ultimately, a case study can allow the researcher to gain insight into a particular object of inquiry and develop a theoretical framework relevant to the research inquiry.

Why use case studies in qualitative research?

Using case studies as a research strategy depends mainly on the nature of the research question and the researcher's access to the data.

Conducting case study research provides a level of detail and contextual richness that other research methods might not offer. They are beneficial when there's a need to understand complex social phenomena within their natural contexts.

The explanatory, exploratory, and descriptive roles of case studies

Case studies can take on various roles depending on the research objectives. They can be exploratory when the research aims to discover new phenomena or define new research questions; they are descriptive when the objective is to depict a phenomenon within its context in a detailed manner; and they can be explanatory if the goal is to understand specific relationships within the studied context. Thus, the versatility of case studies allows researchers to approach their topic from different angles, offering multiple ways to uncover and interpret the data .

The impact of case studies on knowledge development

Case studies play a significant role in knowledge development across various disciplines. Analysis of cases provides an avenue for researchers to explore phenomena within their context based on the collected data.

This can result in the production of rich, practical insights that can be instrumental in both theory-building and practice. Case studies allow researchers to delve into the intricacies and complexities of real-life situations, uncovering insights that might otherwise remain hidden.

Types of case studies

In qualitative research , a case study is not a one-size-fits-all approach. Depending on the nature of the research question and the specific objectives of the study, researchers might choose to use different types of case studies. These types differ in their focus, methodology, and the level of detail they provide about the phenomenon under investigation.

Understanding these types is crucial for selecting the most appropriate approach for your research project and effectively achieving your research goals. Let's briefly look at the main types of case studies.

Exploratory case studies

Exploratory case studies are typically conducted to develop a theory or framework around an understudied phenomenon. They can also serve as a precursor to a larger-scale research project. Exploratory case studies are useful when a researcher wants to identify the key issues or questions which can spur more extensive study or be used to develop propositions for further research. These case studies are characterized by flexibility, allowing researchers to explore various aspects of a phenomenon as they emerge, which can also form the foundation for subsequent studies.

Descriptive case studies

Descriptive case studies aim to provide a complete and accurate representation of a phenomenon or event within its context. These case studies are often based on an established theoretical framework, which guides how data is collected and analyzed. The researcher is concerned with describing the phenomenon in detail, as it occurs naturally, without trying to influence or manipulate it.

Explanatory case studies

Explanatory case studies are focused on explanation - they seek to clarify how or why certain phenomena occur. Often used in complex, real-life situations, they can be particularly valuable in clarifying causal relationships among concepts and understanding the interplay between different factors within a specific context.

Intrinsic, instrumental, and collective case studies

These three categories of case studies focus on the nature and purpose of the study. An intrinsic case study is conducted when a researcher has an inherent interest in the case itself. Instrumental case studies are employed when the case is used to provide insight into a particular issue or phenomenon. A collective case study, on the other hand, involves studying multiple cases simultaneously to investigate some general phenomena.

Each type of case study serves a different purpose and has its own strengths and challenges. The selection of the type should be guided by the research question and objectives, as well as the context and constraints of the research.

The flexibility, depth, and contextual richness offered by case studies make this approach an excellent research method for various fields of study. They enable researchers to investigate real-world phenomena within their specific contexts, capturing nuances that other research methods might miss. Across numerous fields, case studies provide valuable insights into complex issues.

Critical information systems research

Case studies provide a detailed understanding of the role and impact of information systems in different contexts. They offer a platform to explore how information systems are designed, implemented, and used and how they interact with various social, economic, and political factors. Case studies in this field often focus on examining the intricate relationship between technology, organizational processes, and user behavior, helping to uncover insights that can inform better system design and implementation.

Health research

Health research is another field where case studies are highly valuable. They offer a way to explore patient experiences, healthcare delivery processes, and the impact of various interventions in a real-world context.

Case studies can provide a deep understanding of a patient's journey, giving insights into the intricacies of disease progression, treatment effects, and the psychosocial aspects of health and illness.

Asthma research studies

Specifically within medical research, studies on asthma often employ case studies to explore the individual and environmental factors that influence asthma development, management, and outcomes. A case study can provide rich, detailed data about individual patients' experiences, from the triggers and symptoms they experience to the effectiveness of various management strategies. This can be crucial for developing patient-centered asthma care approaches.

Other fields

Apart from the fields mentioned, case studies are also extensively used in business and management research, education research, and political sciences, among many others. They provide an opportunity to delve into the intricacies of real-world situations, allowing for a comprehensive understanding of various phenomena.

Case studies, with their depth and contextual focus, offer unique insights across these varied fields. They allow researchers to illuminate the complexities of real-life situations, contributing to both theory and practice.

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Understanding the key elements of case study design is crucial for conducting rigorous and impactful case study research. A well-structured design guides the researcher through the process, ensuring that the study is methodologically sound and its findings are reliable and valid. The main elements of case study design include the research question , propositions, units of analysis, and the logic linking the data to the propositions.

The research question is the foundation of any research study. A good research question guides the direction of the study and informs the selection of the case, the methods of collecting data, and the analysis techniques. A well-formulated research question in case study research is typically clear, focused, and complex enough to merit further detailed examination of the relevant case(s).

Propositions

Propositions, though not necessary in every case study, provide a direction by stating what we might expect to find in the data collected. They guide how data is collected and analyzed by helping researchers focus on specific aspects of the case. They are particularly important in explanatory case studies, which seek to understand the relationships among concepts within the studied phenomenon.

Units of analysis

The unit of analysis refers to the case, or the main entity or entities that are being analyzed in the study. In case study research, the unit of analysis can be an individual, a group, an organization, a decision, an event, or even a time period. It's crucial to clearly define the unit of analysis, as it shapes the qualitative data analysis process by allowing the researcher to analyze a particular case and synthesize analysis across multiple case studies to draw conclusions.

Argumentation

This refers to the inferential model that allows researchers to draw conclusions from the data. The researcher needs to ensure that there is a clear link between the data, the propositions (if any), and the conclusions drawn. This argumentation is what enables the researcher to make valid and credible inferences about the phenomenon under study.

Understanding and carefully considering these elements in the design phase of a case study can significantly enhance the quality of the research. It can help ensure that the study is methodologically sound and its findings contribute meaningful insights about the case.

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Conducting a case study involves several steps, from defining the research question and selecting the case to collecting and analyzing data . This section outlines these key stages, providing a practical guide on how to conduct case study research.

Defining the research question

The first step in case study research is defining a clear, focused research question. This question should guide the entire research process, from case selection to analysis. It's crucial to ensure that the research question is suitable for a case study approach. Typically, such questions are exploratory or descriptive in nature and focus on understanding a phenomenon within its real-life context.

Selecting and defining the case

The selection of the case should be based on the research question and the objectives of the study. It involves choosing a unique example or a set of examples that provide rich, in-depth data about the phenomenon under investigation. After selecting the case, it's crucial to define it clearly, setting the boundaries of the case, including the time period and the specific context.

Previous research can help guide the case study design. When considering a case study, an example of a case could be taken from previous case study research and used to define cases in a new research inquiry. Considering recently published examples can help understand how to select and define cases effectively.

Developing a detailed case study protocol

A case study protocol outlines the procedures and general rules to be followed during the case study. This includes the data collection methods to be used, the sources of data, and the procedures for analysis. Having a detailed case study protocol ensures consistency and reliability in the study.

The protocol should also consider how to work with the people involved in the research context to grant the research team access to collecting data. As mentioned in previous sections of this guide, establishing rapport is an essential component of qualitative research as it shapes the overall potential for collecting and analyzing data.

Collecting data

Gathering data in case study research often involves multiple sources of evidence, including documents, archival records, interviews, observations, and physical artifacts. This allows for a comprehensive understanding of the case. The process for gathering data should be systematic and carefully documented to ensure the reliability and validity of the study.

Analyzing and interpreting data

The next step is analyzing the data. This involves organizing the data , categorizing it into themes or patterns , and interpreting these patterns to answer the research question. The analysis might also involve comparing the findings with prior research or theoretical propositions.

Writing the case study report

The final step is writing the case study report . This should provide a detailed description of the case, the data, the analysis process, and the findings. The report should be clear, organized, and carefully written to ensure that the reader can understand the case and the conclusions drawn from it.

Each of these steps is crucial in ensuring that the case study research is rigorous, reliable, and provides valuable insights about the case.

The type, depth, and quality of data in your study can significantly influence the validity and utility of the study. In case study research, data is usually collected from multiple sources to provide a comprehensive and nuanced understanding of the case. This section will outline the various methods of collecting data used in case study research and discuss considerations for ensuring the quality of the data.

Interviews are a common method of gathering data in case study research. They can provide rich, in-depth data about the perspectives, experiences, and interpretations of the individuals involved in the case. Interviews can be structured , semi-structured , or unstructured , depending on the research question and the degree of flexibility needed.

Observations

Observations involve the researcher observing the case in its natural setting, providing first-hand information about the case and its context. Observations can provide data that might not be revealed in interviews or documents, such as non-verbal cues or contextual information.

Documents and artifacts

Documents and archival records provide a valuable source of data in case study research. They can include reports, letters, memos, meeting minutes, email correspondence, and various public and private documents related to the case.

These records can provide historical context, corroborate evidence from other sources, and offer insights into the case that might not be apparent from interviews or observations.

Physical artifacts refer to any physical evidence related to the case, such as tools, products, or physical environments. These artifacts can provide tangible insights into the case, complementing the data gathered from other sources.

Ensuring the quality of data collection

Determining the quality of data in case study research requires careful planning and execution. It's crucial to ensure that the data is reliable, accurate, and relevant to the research question. This involves selecting appropriate methods of collecting data, properly training interviewers or observers, and systematically recording and storing the data. It also includes considering ethical issues related to collecting and handling data, such as obtaining informed consent and ensuring the privacy and confidentiality of the participants.

Data analysis

Analyzing case study research involves making sense of the rich, detailed data to answer the research question. This process can be challenging due to the volume and complexity of case study data. However, a systematic and rigorous approach to analysis can ensure that the findings are credible and meaningful. This section outlines the main steps and considerations in analyzing data in case study research.

Organizing the data

The first step in the analysis is organizing the data. This involves sorting the data into manageable sections, often according to the data source or the theme. This step can also involve transcribing interviews, digitizing physical artifacts, or organizing observational data.

Categorizing and coding the data

Once the data is organized, the next step is to categorize or code the data. This involves identifying common themes, patterns, or concepts in the data and assigning codes to relevant data segments. Coding can be done manually or with the help of software tools, and in either case, qualitative analysis software can greatly facilitate the entire coding process. Coding helps to reduce the data to a set of themes or categories that can be more easily analyzed.

Identifying patterns and themes

After coding the data, the researcher looks for patterns or themes in the coded data. This involves comparing and contrasting the codes and looking for relationships or patterns among them. The identified patterns and themes should help answer the research question.

Interpreting the data

Once patterns and themes have been identified, the next step is to interpret these findings. This involves explaining what the patterns or themes mean in the context of the research question and the case. This interpretation should be grounded in the data, but it can also involve drawing on theoretical concepts or prior research.

Verification of the data

The last step in the analysis is verification. This involves checking the accuracy and consistency of the analysis process and confirming that the findings are supported by the data. This can involve re-checking the original data, checking the consistency of codes, or seeking feedback from research participants or peers.

Like any research method , case study research has its strengths and limitations. Researchers must be aware of these, as they can influence the design, conduct, and interpretation of the study.

Understanding the strengths and limitations of case study research can also guide researchers in deciding whether this approach is suitable for their research question . This section outlines some of the key strengths and limitations of case study research.

Benefits include the following:

• Rich, detailed data: One of the main strengths of case study research is that it can generate rich, detailed data about the case. This can provide a deep understanding of the case and its context, which can be valuable in exploring complex phenomena.
• Flexibility: Case study research is flexible in terms of design , data collection , and analysis . A sufficient degree of flexibility allows the researcher to adapt the study according to the case and the emerging findings.
• Real-world context: Case study research involves studying the case in its real-world context, which can provide valuable insights into the interplay between the case and its context.
• Multiple sources of evidence: Case study research often involves collecting data from multiple sources , which can enhance the robustness and validity of the findings.

On the other hand, researchers should consider the following limitations:

• Generalizability: A common criticism of case study research is that its findings might not be generalizable to other cases due to the specificity and uniqueness of each case.
• Time and resource intensive: Case study research can be time and resource intensive due to the depth of the investigation and the amount of collected data.
• Complexity of analysis: The rich, detailed data generated in case study research can make analyzing the data challenging.
• Subjectivity: Given the nature of case study research, there may be a higher degree of subjectivity in interpreting the data , so researchers need to reflect on this and transparently convey to audiences how the research was conducted.

Being aware of these strengths and limitations can help researchers design and conduct case study research effectively and interpret and report the findings appropriately.

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Designing and Conducting Case Studies

This guide examines case studies, a form of qualitative descriptive research that is used to look at individuals, a small group of participants, or a group as a whole. Researchers collect data about participants using participant and direct observations, interviews, protocols, tests, examinations of records, and collections of writing samples. Starting with a definition of the case study, the guide moves to a brief history of this research method. Using several well documented case studies, the guide then looks at applications and methods including data collection and analysis. A discussion of ways to handle validity, reliability, and generalizability follows, with special attention to case studies as they are applied to composition studies. Finally, this guide examines the strengths and weaknesses of case studies.

Definition and Overview

Case study refers to the collection and presentation of detailed information about a particular participant or small group, frequently including the accounts of subjects themselves. A form of qualitative descriptive research, the case study looks intensely at an individual or small participant pool, drawing conclusions only about that participant or group and only in that specific context. Researchers do not focus on the discovery of a universal, generalizable truth, nor do they typically look for cause-effect relationships; instead, emphasis is placed on exploration and description.

Case studies typically examine the interplay of all variables in order to provide as complete an understanding of an event or situation as possible. This type of comprehensive understanding is arrived at through a process known as thick description, which involves an in-depth description of the entity being evaluated, the circumstances under which it is used, the characteristics of the people involved in it, and the nature of the community in which it is located. Thick description also involves interpreting the meaning of demographic and descriptive data such as cultural norms and mores, community values, ingrained attitudes, and motives.

Unlike quantitative methods of research, like the survey, which focus on the questions of who, what, where, how much, and how many, and archival analysis, which often situates the participant in some form of historical context, case studies are the preferred strategy when how or why questions are asked. Likewise, they are the preferred method when the researcher has little control over the events, and when there is a contemporary focus within a real life context. In addition, unlike more specifically directed experiments, case studies require a problem that seeks a holistic understanding of the event or situation in question using inductive logic--reasoning from specific to more general terms.

In scholarly circles, case studies are frequently discussed within the context of qualitative research and naturalistic inquiry. Case studies are often referred to interchangeably with ethnography, field study, and participant observation. The underlying philosophical assumptions in the case are similar to these types of qualitative research because each takes place in a natural setting (such as a classroom, neighborhood, or private home), and strives for a more holistic interpretation of the event or situation under study.

Unlike more statistically-based studies which search for quantifiable data, the goal of a case study is to offer new variables and questions for further research. F.H. Giddings, a sociologist in the early part of the century, compares statistical methods to the case study on the basis that the former are concerned with the distribution of a particular trait, or a small number of traits, in a population, whereas the case study is concerned with the whole variety of traits to be found in a particular instance" (Hammersley 95).

Case studies are not a new form of research; naturalistic inquiry was the primary research tool until the development of the scientific method. The fields of sociology and anthropology are credited with the primary shaping of the concept as we know it today. However, case study research has drawn from a number of other areas as well: the clinical methods of doctors; the casework technique being developed by social workers; the methods of historians and anthropologists, plus the qualitative descriptions provided by quantitative researchers like LePlay; and, in the case of Robert Park, the techniques of newspaper reporters and novelists.

Park was an ex-newspaper reporter and editor who became very influential in developing sociological case studies at the University of Chicago in the 1920s. As a newspaper professional he coined the term "scientific" or "depth" reporting: the description of local events in a way that pointed to major social trends. Park viewed the sociologist as "merely a more accurate, responsible, and scientific reporter." Park stressed the variety and value of human experience. He believed that sociology sought to arrive at natural, but fluid, laws and generalizations in regard to human nature and society. These laws weren't static laws of the kind sought by many positivists and natural law theorists, but rather, they were laws of becoming--with a constant possibility of change. Park encouraged students to get out of the library, to quit looking at papers and books, and to view the constant experiment of human experience. He writes, "Go and sit in the lounges of the luxury hotels and on the doorsteps of the flophouses; sit on the Gold Coast settees and on the slum shakedowns; sit in the Orchestra Hall and in the Star and Garter Burlesque. In short, gentlemen [sic], go get the seats of your pants dirty in real research."

But over the years, case studies have drawn their share of criticism. In fact, the method had its detractors from the start. In the 1920s, the debate between pro-qualitative and pro-quantitative became quite heated. Case studies, when compared to statistics, were considered by many to be unscientific. From the 1930's on, the rise of positivism had a growing influence on quantitative methods in sociology. People wanted static, generalizable laws in science. The sociological positivists were looking for stable laws of social phenomena. They criticized case study research because it failed to provide evidence of inter subjective agreement. Also, they condemned it because of the few number of cases studied and that the under-standardized character of their descriptions made generalization impossible. By the 1950s, quantitative methods, in the form of survey research, had become the dominant sociological approach and case study had become a minority practice.

Educational Applications

The 1950's marked the dawning of a new era in case study research, namely that of the utilization of the case study as a teaching method. "Instituted at Harvard Business School in the 1950s as a primary method of teaching, cases have since been used in classrooms and lecture halls alike, either as part of a course of study or as the main focus of the course to which other teaching material is added" (Armisted 1984). The basic purpose of instituting the case method as a teaching strategy was "to transfer much of the responsibility for learning from the teacher on to the student, whose role, as a result, shifts away from passive absorption toward active construction" (Boehrer 1990). Through careful examination and discussion of various cases, "students learn to identify actual problems, to recognize key players and their agendas, and to become aware of those aspects of the situation that contribute to the problem" (Merseth 1991). In addition, students are encouraged to "generate their own analysis of the problems under consideration, to develop their own solutions, and to practically apply their own knowledge of theory to these problems" (Boyce 1993). Along the way, students also develop "the power to analyze and to master a tangled circumstance by identifying and delineating important factors; the ability to utilize ideas, to test them against facts, and to throw them into fresh combinations" (Merseth 1991).

In addition to the practical application and testing of scholarly knowledge, case discussions can also help students prepare for real-world problems, situations and crises by providing an approximation of various professional environments (i.e. classroom, board room, courtroom, or hospital). Thus, through the examination of specific cases, students are given the opportunity to work out their own professional issues through the trials, tribulations, experiences, and research findings of others. An obvious advantage to this mode of instruction is that it allows students the exposure to settings and contexts that they might not otherwise experience. For example, a student interested in studying the effects of poverty on minority secondary student's grade point averages and S.A.T. scores could access and analyze information from schools as geographically diverse as Los Angeles, New York City, Miami, and New Mexico without ever having to leave the classroom.

The case study method also incorporates the idea that students can learn from one another "by engaging with each other and with each other's ideas, by asserting something and then having it questioned, challenged and thrown back at them so that they can reflect on what they hear, and then refine what they say" (Boehrer 1990). In summary, students can direct their own learning by formulating questions and taking responsibility for the study.

Types and Design Concerns

Researchers use multiple methods and approaches to conduct case studies.

Types of Case Studies

Under the more generalized category of case study exist several subdivisions, each of which is custom selected for use depending upon the goals and/or objectives of the investigator. These types of case study include the following:

Illustrative Case Studies These are primarily descriptive studies. They typically utilize one or two instances of an event to show what a situation is like. Illustrative case studies serve primarily to make the unfamiliar familiar and to give readers a common language about the topic in question.

Exploratory (or pilot) Case Studies These are condensed case studies performed before implementing a large scale investigation. Their basic function is to help identify questions and select types of measurement prior to the main investigation. The primary pitfall of this type of study is that initial findings may seem convincing enough to be released prematurely as conclusions.

Cumulative Case Studies These serve to aggregate information from several sites collected at different times. The idea behind these studies is the collection of past studies will allow for greater generalization without additional cost or time being expended on new, possibly repetitive studies.

Critical Instance Case Studies These examine one or more sites for either the purpose of examining a situation of unique interest with little to no interest in generalizability, or to call into question or challenge a highly generalized or universal assertion. This method is useful for answering cause and effect questions.

Identifying a Theoretical Perspective

Much of the case study's design is inherently determined for researchers, depending on the field from which they are working. In composition studies, researchers are typically working from a qualitative, descriptive standpoint. In contrast, physicists will approach their research from a more quantitative perspective. Still, in designing the study, researchers need to make explicit the questions to be explored and the theoretical perspective from which they will approach the case. The three most commonly adopted theories are listed below:

Individual Theories These focus primarily on the individual development, cognitive behavior, personality, learning and disability, and interpersonal interactions of a particular subject.

Organizational Theories These focus on bureaucracies, institutions, organizational structure and functions, or excellence in organizational performance.

Social Theories These focus on urban development, group behavior, cultural institutions, or marketplace functions.

Two examples of case studies are used consistently throughout this chapter. The first, a study produced by Berkenkotter, Huckin, and Ackerman (1988), looks at a first year graduate student's initiation into an academic writing program. The study uses participant-observer and linguistic data collecting techniques to assess the student's knowledge of appropriate discourse conventions. Using the pseudonym Nate to refer to the subject, the study sought to illuminate the particular experience rather than to generalize about the experience of fledgling academic writers collectively.

For example, in Berkenkotter, Huckin, and Ackerman's (1988) study we are told that the researchers are interested in disciplinary communities. In the first paragraph, they ask what constitutes membership in a disciplinary community and how achieving membership might affect a writer's understanding and production of texts. In the third paragraph they state that researchers must negotiate their claims "within the context of his sub specialty's accepted knowledge and methodology." In the next paragraph they ask, "How is literacy acquired? What is the process through which novices gain community membership? And what factors either aid or hinder students learning the requisite linguistic behaviors?" This introductory section ends with a paragraph in which the study's authors claim that during the course of the study, the subject, Nate, successfully makes the transition from "skilled novice" to become an initiated member of the academic discourse community and that his texts exhibit linguistic changes which indicate this transition. In the next section the authors make explicit the sociolinguistic theoretical and methodological assumptions on which the study is based (1988). Thus the reader has a good understanding of the authors' theoretical background and purpose in conducting the study even before it is explicitly stated on the fourth page of the study. "Our purpose was to examine the effects of the educational context on one graduate student's production of texts as he wrote in different courses and for different faculty members over the academic year 1984-85." The goal of the study then, was to explore the idea that writers must be initiated into a writing community, and that this initiation will change the way one writes.

The second example is Janet Emig's (1971) study of the composing process of a group of twelfth graders. In this study, Emig seeks to answer the question of what happens to the self as a result educational stimuli in terms of academic writing. The case study used methods such as protocol analysis, tape-recorded interviews, and discourse analysis.

In the case of Janet Emig's (1971) study of the composing process of eight twelfth graders, four specific hypotheses were made:

• Twelfth grade writers engage in two modes of composing: reflexive and extensive.
• These differences can be ascertained and characterized through having the writers compose aloud their composition process.
• A set of implied stylistic principles governs the writing process.
• For twelfth grade writers, extensive writing occurs chiefly as a school-sponsored activity, or reflexive, as a self-sponsored activity.

In this study, the chief distinction is between the two dominant modes of composing among older, secondary school students. The distinctions are:

• The reflexive mode, which focuses on the writer's thoughts and feelings.
• The extensive mode, which focuses on conveying a message.

Emig also outlines the specific questions which guided the research in the opening pages of her Review of Literature , preceding the report.

Designing a Case Study

After considering the different sub categories of case study and identifying a theoretical perspective, researchers can begin to design their study. Research design is the string of logic that ultimately links the data to be collected and the conclusions to be drawn to the initial questions of the study. Typically, research designs deal with at least four problems:

• What questions to study
• What data are relevant
• What data to collect
• How to analyze that data

In other words, a research design is basically a blueprint for getting from the beginning to the end of a study. The beginning is an initial set of questions to be answered, and the end is some set of conclusions about those questions.

Because case studies are conducted on topics as diverse as Anglo-Saxon Literature (Thrane 1986) and AIDS prevention (Van Vugt 1994), it is virtually impossible to outline any strict or universal method or design for conducting the case study. However, Robert K. Yin (1993) does offer five basic components of a research design:

• A study's questions.
• A study's propositions (if any).
• A study's units of analysis.
• The logic that links the data to the propositions.
• The criteria for interpreting the findings.

In addition to these five basic components, Yin also stresses the importance of clearly articulating one's theoretical perspective, determining the goals of the study, selecting one's subject(s), selecting the appropriate method(s) of collecting data, and providing some considerations to the composition of the final report.

Conducting Case Studies

To obtain as complete a picture of the participant as possible, case study researchers can employ a variety of approaches and methods. These approaches, methods, and related issues are discussed in depth in this section.

Method: Single or Multi-modal?

To obtain as complete a picture of the participant as possible, case study researchers can employ a variety of methods. Some common methods include interviews , protocol analyses, field studies, and participant-observations. Emig (1971) chose to use several methods of data collection. Her sources included conversations with the students, protocol analysis, discrete observations of actual composition, writing samples from each student, and school records (Lauer and Asher 1988).

Berkenkotter, Huckin, and Ackerman (1988) collected data by observing classrooms, conducting faculty and student interviews, collecting self reports from the subject, and by looking at the subject's written work.

A study that was criticized for using a single method model was done by Flower and Hayes (1984). In this study that explores the ways in which writers use different forms of knowing to create space, the authors used only protocol analysis to gather data. The study came under heavy fire because of their decision to use only one method.

Participant Selection

Case studies can use one participant, or a small group of participants. However, it is important that the participant pool remain relatively small. The participants can represent a diverse cross section of society, but this isn't necessary.

For example, the Berkenkotter, Huckin, and Ackerman (1988) study looked at just one participant, Nate. By contrast, in Janet Emig's (1971) study of the composition process of twelfth graders, eight participants were selected representing a diverse cross section of the community, with volunteers from an all-white upper-middle-class suburban school, an all-black inner-city school, a racially mixed lower-middle-class school, an economically and racially mixed school, and a university school.

Often, a brief "case history" is done on the participants of the study in order to provide researchers with a clearer understanding of their participants, as well as some insight as to how their own personal histories might affect the outcome of the study. For instance, in Emig's study, the investigator had access to the school records of five of the participants, and to standardized test scores for the remaining three. Also made available to the researcher was the information that three of the eight students were selected as NCTE Achievement Award winners. These personal histories can be useful in later stages of the study when data are being analyzed and conclusions drawn.

Data Collection

There are six types of data collected in case studies:

• Archival records.
• Interviews.
• Direct observation.
• Participant observation.

In the field of composition research, these six sources might be:

• A writer's drafts.
• School records of student writers.
• Transcripts of interviews with a writer.
• Transcripts of conversations between writers (and protocols).
• Videotapes and notes from direct field observations.
• Hard copies of a writer's work on computer.

Depending on whether researchers have chosen to use a single or multi-modal approach for the case study, they may choose to collect data from one or any combination of these sources.

Protocols, that is, transcriptions of participants talking aloud about what they are doing as they do it, have been particularly common in composition case studies. For example, in Emig's (1971) study, the students were asked, in four different sessions, to give oral autobiographies of their writing experiences and to compose aloud three themes in the presence of a tape recorder and the investigator.

In some studies, only one method of data collection is conducted. For example, the Flower and Hayes (1981) report on the cognitive process theory of writing depends on protocol analysis alone. However, using multiple sources of evidence to increase the reliability and validity of the data can be advantageous.

Case studies are likely to be much more convincing and accurate if they are based on several different sources of information, following a corroborating mode. This conclusion is echoed among many composition researchers. For example, in her study of predrafting processes of high and low-apprehensive writers, Cynthia Selfe (1985) argues that because "methods of indirect observation provide only an incomplete reflection of the complex set of processes involved in composing, a combination of several such methods should be used to gather data in any one study." Thus, in this study, Selfe collected her data from protocols, observations of students role playing their writing processes, audio taped interviews with the students, and videotaped observations of the students in the process of composing.

It can be said then, that cross checking data from multiple sources can help provide a multidimensional profile of composing activities in a particular setting. Sharan Merriam (1985) suggests "checking, verifying, testing, probing, and confirming collected data as you go, arguing that this process will follow in a funnel-like design resulting in less data gathering in later phases of the study along with a congruent increase in analysis checking, verifying, and confirming."

It is important to note that in case studies, as in any qualitative descriptive research, while researchers begin their studies with one or several questions driving the inquiry (which influence the key factors the researcher will be looking for during data collection), a researcher may find new key factors emerging during data collection. These might be unexpected patterns or linguistic features which become evident only during the course of the research. While not bearing directly on the researcher's guiding questions, these variables may become the basis for new questions asked at the end of the report, thus linking to the possibility of further research.

Data Analysis

As the information is collected, researchers strive to make sense of their data. Generally, researchers interpret their data in one of two ways: holistically or through coding. Holistic analysis does not attempt to break the evidence into parts, but rather to draw conclusions based on the text as a whole. Flower and Hayes (1981), for example, make inferences from entire sections of their students' protocols, rather than searching through the transcripts to look for isolatable characteristics.

However, composition researchers commonly interpret their data by coding, that is by systematically searching data to identify and/or categorize specific observable actions or characteristics. These observable actions then become the key variables in the study. Sharan Merriam (1988) suggests seven analytic frameworks for the organization and presentation of data:

• The role of participants.
• The network analysis of formal and informal exchanges among groups.
• Historical.
• Thematical.
• Ritual and symbolism.
• Critical incidents that challenge or reinforce fundamental beliefs, practices, and values.

There are two purposes of these frameworks: to look for patterns among the data and to look for patterns that give meaning to the case study.

As stated above, while most researchers begin their case studies expecting to look for particular observable characteristics, it is not unusual for key variables to emerge during data collection. Typical variables coded in case studies of writers include pauses writers make in the production of a text, the use of specific linguistic units (such as nouns or verbs), and writing processes (planning, drafting, revising, and editing). In the Berkenkotter, Huckin, and Ackerman (1988) study, for example, researchers coded the participant's texts for use of connectives, discourse demonstratives, average sentence length, off-register words, use of the first person pronoun, and the ratio of definite articles to indefinite articles.

Since coding is inherently subjective, more than one coder is usually employed. In the Berkenkotter, Huckin, and Ackerman (1988) study, for example, three rhetoricians were employed to code the participant's texts for off-register phrases. The researchers established the agreement among the coders before concluding that the participant used fewer off-register words as the graduate program progressed.

Composing the Case Study Report

In the many forms it can take, "a case study is generically a story; it presents the concrete narrative detail of actual, or at least realistic events, it has a plot, exposition, characters, and sometimes even dialogue" (Boehrer 1990). Generally, case study reports are extensively descriptive, with "the most problematic issue often referred to as being the determination of the right combination of description and analysis" (1990). Typically, authors address each step of the research process, and attempt to give the reader as much context as possible for the decisions made in the research design and for the conclusions drawn.

This contextualization usually includes a detailed explanation of the researchers' theoretical positions, of how those theories drove the inquiry or led to the guiding research questions, of the participants' backgrounds, of the processes of data collection, of the training and limitations of the coders, along with a strong attempt to make connections between the data and the conclusions evident.

Although the Berkenkotter, Huckin, and Ackerman (1988) study does not, case study reports often include the reactions of the participants to the study or to the researchers' conclusions. Because case studies tend to be exploratory, most end with implications for further study. Here researchers may identify significant variables that emerged during the research and suggest studies related to these, or the authors may suggest further general questions that their case study generated.

For example, Emig's (1971) study concludes with a section dedicated solely to the topic of implications for further research, in which she suggests several means by which this particular study could have been improved, as well as questions and ideas raised by this study which other researchers might like to address, such as: is there a correlation between a certain personality and a certain composing process profile (e.g. is there a positive correlation between ego strength and persistence in revising)?

Also included in Emig's study is a section dedicated to implications for teaching, which outlines the pedagogical ramifications of the study's findings for teachers currently involved in high school writing programs.

Sharan Merriam (1985) also offers several suggestions for alternative presentations of data:

• Prepare specialized condensations for appropriate groups.
• Replace narrative sections with a series of answers to open-ended questions.
• Present "skimmer's" summaries at beginning of each section.
• Incorporate headlines that encapsulate information from text.
• Prepare analytic summaries with supporting data appendixes.
• Present data in colorful and/or unique graphic representations.

Issues of Validity and Reliability

Once key variables have been identified, they can be analyzed. Reliability becomes a key concern at this stage, and many case study researchers go to great lengths to ensure that their interpretations of the data will be both reliable and valid. Because issues of validity and reliability are an important part of any study in the social sciences, it is important to identify some ways of dealing with results.

Multi-modal case study researchers often balance the results of their coding with data from interviews or writer's reflections upon their own work. Consequently, the researchers' conclusions become highly contextualized. For example, in a case study which looked at the time spent in different stages of the writing process, Berkenkotter concluded that her participant, Donald Murray, spent more time planning his essays than in other writing stages. The report of this case study is followed by Murray's reply, wherein he agrees with some of Berkenkotter's conclusions and disagrees with others.

As is the case with other research methodologies, issues of external validity, construct validity, and reliability need to be carefully considered.

Commentary on Case Studies

Researchers often debate the relative merits of particular methods, among them case study. In this section, we comment on two key issues. To read the commentaries, choose any of the items below:

Strengths and Weaknesses of Case Studies

Most case study advocates point out that case studies produce much more detailed information than what is available through a statistical analysis. Advocates will also hold that while statistical methods might be able to deal with situations where behavior is homogeneous and routine, case studies are needed to deal with creativity, innovation, and context. Detractors argue that case studies are difficult to generalize because of inherent subjectivity and because they are based on qualitative subjective data, generalizable only to a particular context.

Flexibility

The case study approach is a comparatively flexible method of scientific research. Because its project designs seem to emphasize exploration rather than prescription or prediction, researchers are comparatively freer to discover and address issues as they arise in their experiments. In addition, the looser format of case studies allows researchers to begin with broad questions and narrow their focus as their experiment progresses rather than attempt to predict every possible outcome before the experiment is conducted.

Emphasis on Context

By seeking to understand as much as possible about a single subject or small group of subjects, case studies specialize in "deep data," or "thick description"--information based on particular contexts that can give research results a more human face. This emphasis can help bridge the gap between abstract research and concrete practice by allowing researchers to compare their firsthand observations with the quantitative results obtained through other methods of research.

Inherent Subjectivity

"The case study has long been stereotyped as the weak sibling among social science methods," and is often criticized as being too subjective and even pseudo-scientific. Likewise, "investigators who do case studies are often regarded as having deviated from their academic disciplines, and their investigations as having insufficient precision (that is, quantification), objectivity and rigor" (Yin 1989). Opponents cite opportunities for subjectivity in the implementation, presentation, and evaluation of case study research. The approach relies on personal interpretation of data and inferences. Results may not be generalizable, are difficult to test for validity, and rarely offer a problem-solving prescription. Simply put, relying on one or a few subjects as a basis for cognitive extrapolations runs the risk of inferring too much from what might be circumstance.

High Investment

Case studies can involve learning more about the subjects being tested than most researchers would care to know--their educational background, emotional background, perceptions of themselves and their surroundings, their likes, dislikes, and so on. Because of its emphasis on "deep data," the case study is out of reach for many large-scale research projects which look at a subject pool in the tens of thousands. A budget request of $10,000 to examine 200 subjects sounds more efficient than a similar request to examine four subjects.

Ethical Considerations

Researchers conducting case studies should consider certain ethical issues. For example, many educational case studies are often financed by people who have, either directly or indirectly, power over both those being studied and those conducting the investigation (1985). This conflict of interests can hinder the credibility of the study.

The personal integrity, sensitivity, and possible prejudices and/or biases of the investigators need to be taken into consideration as well. Personal biases can creep into how the research is conducted, alternative research methods used, and the preparation of surveys and questionnaires.

A common complaint in case study research is that investigators change direction during the course of the study unaware that their original research design was inadequate for the revised investigation. Thus, the researchers leave unknown gaps and biases in the study. To avoid this, researchers should report preliminary findings so that the likelihood of bias will be reduced.

Concerns about Reliability, Validity, and Generalizability

Merriam (1985) offers several suggestions for how case study researchers might actively combat the popular attacks on the validity, reliability, and generalizability of case studies:

• Prolong the Processes of Data Gathering on Site: This will help to insure the accuracy of the findings by providing the researcher with more concrete information upon which to formulate interpretations.
• Employ the Process of "Triangulation": Use a variety of data sources as opposed to relying solely upon one avenue of observation. One example of such a data check would be what McClintock, Brannon, and Maynard (1985) refer to as a "case cluster method," that is, when a single unit within a larger case is randomly sampled, and that data treated quantitatively." For instance, in Emig's (1971) study, the case cluster method was employed, singling out the productivity of a single student named Lynn. This cluster profile included an advanced case history of the subject, specific examination and analysis of individual compositions and protocols, and extensive interview sessions. The seven remaining students were then compared with the case of Lynn, to ascertain if there are any shared, or unique dimensions to the composing process engaged in by these eight students.
• Conduct Member Checks: Initiate and maintain an active corroboration on the interpretation of data between the researcher and those who provided the data. In other words, talk to your subjects.
• Collect Referential Materials: Complement the file of materials from the actual site with additional document support. For example, Emig (1971) supports her initial propositions with historical accounts by writers such as T.S. Eliot, James Joyce, and D.H. Lawrence. Emig also cites examples of theoretical research done with regards to the creative process, as well as examples of empirical research dealing with the writing of adolescents. Specific attention is then given to the four stages description of the composing process delineated by Helmoltz, Wallas, and Cowley, as it serves as the focal point in this study.
• Engage in Peer Consultation: Prior to composing the final draft of the report, researchers should consult with colleagues in order to establish validity through pooled judgment.

Although little can be done to combat challenges concerning the generalizability of case studies, "most writers suggest that qualitative research should be judged as credible and confirmable as opposed to valid and reliable" (Merriam 1985). Likewise, it has been argued that "rather than transplanting statistical, quantitative notions of generalizability and thus finding qualitative research inadequate, it makes more sense to develop an understanding of generalization that is congruent with the basic characteristics of qualitative inquiry" (1985). After all, criticizing the case study method for being ungeneralizable is comparable to criticizing a washing machine for not being able to tell the correct time. In other words, it is unjust to criticize a method for not being able to do something which it was never originally designed to do in the first place.

Annotated Bibliography

Armisted, C. (1984). How Useful are Case Studies. Training and Development Journal, 38 (2), 75-77.

This article looks at eight types of case studies, offers pros and cons of using case studies in the classroom, and gives suggestions for successfully writing and using case studies.

Bardovi-Harlig, K. (1997). Beyond Methods: Components of Second Language Teacher Education . New York: McGraw-Hill.

A compilation of various research essays which address issues of language teacher education. Essays included are: "Non-native reading research and theory" by Lee, "The case for Psycholinguistics" by VanPatten, and "Assessment and Second Language Teaching" by Gradman and Reed.

Bartlett, L. (1989). A Question of Good Judgment; Interpretation Theory and Qualitative Enquiry Address. 70th Annual Meeting of the American Educational Research Association. San Francisco.

Bartlett selected "quasi-historical" methodology, which focuses on the "truth" found in case records, as one that will provide "good judgments" in educational inquiry. He argues that although the method is not comprehensive, it can try to connect theory with practice.

Baydere, S. et. al. (1993). Multimedia conferencing as a tool for collaborative writing: a case study in Computer Supported Collaborative Writing. New York: Springer-Verlag.

The case study by Baydere et. al. is just one of the many essays in this book found in the series "Computer Supported Cooperative Work." Denley, Witefield and May explore similar issues in their essay, "A case study in task analysis for the design of a collaborative document production system."

Berkenkotter, C., Huckin, T., N., & Ackerman J. (1988). Conventions, Conversations, and the Writer: Case Study of a Student in a Rhetoric Ph.D. Program. Research in the Teaching of English, 22, 9-44.

The authors focused on how the writing of their subject, Nate or Ackerman, changed as he became more acquainted or familiar with his field's discourse community.

Berninger, V., W., and Gans, B., M. (1986). Language Profiles in Nonspeaking Individuals of Normal Intelligence with Severe Cerebral Palsy. Augmentative and Alternative Communication, 2, 45-50.

Argues that generalizations about language abilities in patients with severe cerebral palsy (CP) should be avoided. Standardized tests of different levels of processing oral language, of processing written language, and of producing written language were administered to 3 male participants (aged 9, 16, and 40 yrs).

Bockman, J., R., and Couture, B. (1984). The Case Method in Technical Communication: Theory and Models. Texas: Association of Teachers of Technical Writing.

Examines the study and teaching of technical writing, communication of technical information, and the case method in terms of those applications.

Boehrer, J. (1990). Teaching With Cases: Learning to Question. New Directions for Teaching and Learning, 42 41-57.

This article discusses the origins of the case method, looks at the question of what is a case, gives ideas about learning in case teaching, the purposes it can serve in the classroom, the ground rules for the case discussion, including the role of the question, and new directions for case teaching.

Bowman, W. R. (1993). Evaluating JTPA Programs for Economically Disadvantaged Adults: A Case Study of Utah and General Findings . Washington: National Commission for Employment Policy.

"To encourage state-level evaluations of JTPA, the Commission and the State of Utah co-sponsored this report on the effectiveness of JTPA Title II programs for adults in Utah. The technique used is non-experimental and the comparison group was selected from registrants with Utah's Employment Security. In a step-by-step approach, the report documents how non-experimental techniques can be applied and several specific technical issues can be addressed."

Boyce, A. (1993) The Case Study Approach for Pedagogists. Annual Meeting of the American Alliance for Health, Physical Education, Recreation and Dance. (Address). Washington DC.

This paper addresses how case studies 1) bridge the gap between teaching theory and application, 2) enable students to analyze problems and develop solutions for situations that will be encountered in the real world of teaching, and 3) helps students to evaluate the feasibility of alternatives and to understand the ramifications of a particular course of action.

Carson, J. (1993) The Case Study: Ideal Home of WAC Quantitative and Qualitative Data. Annual Meeting of the Conference on College Composition and Communication. (Address). San Diego.

"Increasingly, one of the most pressing questions for WAC advocates is how to keep [WAC] programs going in the face of numerous difficulties. Case histories offer the best chance for fashioning rhetorical arguments to keep WAC programs going because they offer the opportunity to provide a coherent narrative that contextualizes all documents and data, including what is generally considered scientific data. A case study of the WAC program, . . . at Robert Morris College in Pittsburgh demonstrates the advantages of this research method. Such studies are ideal homes for both naturalistic and positivistic data as well as both quantitative and qualitative information."

---. (1991). A Cognitive Process Theory of Writing. College Composition and Communication. 32. 365-87.

No abstract available.

Cromer, R. (1994) A Case Study of Dissociations Between Language and Cognition. Constraints on Language Acquisition: Studies of Atypical Children . Hillsdale: Lawrence Erlbaum Associates, 141-153.

Crossley, M. (1983) Case Study in Comparative and International Education: An Approach to Bridging the Theory-Practice Gap. Proceedings of the 11th Annual Conference of the Australian Comparative and International Education Society. Hamilton, NZ.

Case study research, as presented here, helps bridge the theory-practice gap in comparative and international research studies of education because it focuses on the practical, day-to-day context rather than on the national arena. The paper asserts that the case study method can be valuable at all levels of research, formation, and verification of theories in education.

Daillak, R., H., and Alkin, M., C. (1982). Qualitative Studies in Context: Reflections on the CSE Studies of Evaluation Use . California: EDRS

The report shows how the Center of the Study of Evaluation (CSE) applied qualitative techniques to a study of evaluation information use in local, Los Angeles schools. It critiques the effectiveness and the limitations of using case study, evaluation, field study, and user interview survey methodologies.

Davey, L. (1991). The Application of Case Study Evaluations. ERIC/TM Digest.

This article examines six types of case studies, the type of evaluation questions that can be answered, the functions served, some design features, and some pitfalls of the method.

Deutch, C. E. (1996). A course in research ethics for graduate students. College Teaching, 44, 2, 56-60.

This article describes a one-credit discussion course in research ethics for graduate students in biology. Case studies are focused on within the four parts of the course: 1) major issues, 2 )practical issues in scholarly work, 3) ownership of research results, and 4) training and personal decisions.

DeVoss, G. (1981). Ethics in Fieldwork Research. RIE 27p. (ERIC)

This article examines four of the ethical problems that can happen when conducting case study research: acquiring permission to do research, knowing when to stop digging, the pitfalls of doing collaborative research, and preserving the integrity of the participants.

Driscoll, A. (1985). Case Study of a Research Intervention: the University of Utah’s Collaborative Approach . San Francisco: Far West Library for Educational Research Development.

Paper presented at the annual meeting of the American Association of Colleges of Teacher Education, Denver, CO, March 1985. Offers information of in-service training, specifically case studies application.

Ellram, L. M. (1996). The Use of the Case Study Method in Logistics Research. Journal of Business Logistics, 17, 2, 93.

This article discusses the increased use of case study in business research, and the lack of understanding of when and how to use case study methodology in business.

Emig, J. (1971) The Composing Processes of Twelfth Graders . Urbana: NTCE.

This case study uses observation, tape recordings, writing samples, and school records to show that writing in reflexive and extensive situations caused different lengths of discourse and different clusterings of the components of the writing process.

Feagin, J. R. (1991). A Case For the Case Study . Chapel Hill: The University of North Carolina Press.

This book discusses the nature, characteristics, and basic methodological issues of the case study as a research method.

Feldman, H., Holland, A., & Keefe, K. (1989) Language Abilities after Left Hemisphere Brain Injury: A Case Study of Twins. Topics in Early Childhood Special Education, 9, 32-47.

"Describes the language abilities of 2 twin pairs in which 1 twin (the experimental) suffered brain injury to the left cerebral hemisphere around the time of birth and1 twin (the control) did not. One pair of twins was initially assessed at age 23 mo. and the other at about 30 mo.; they were subsequently evaluated in their homes 3 times at about 6-mo intervals."

Fidel, R. (1984). The Case Study Method: A Case Study. Library and Information Science Research, 6.

The article describes the use of case study methodology to systematically develop a model of online searching behavior in which study design is flexible, subject manner determines data gathering and analyses, and procedures adapt to the study's progressive change.

Flower, L., & Hayes, J. R. (1984). Images, Plans and Prose: The Representation of Meaning in Writing. Written Communication, 1, 120-160.

Explores the ways in which writers actually use different forms of knowing to create prose.

Frey, L. R. (1992). Interpreting Communication Research: A Case Study Approach Englewood Cliffs, N.J.: Prentice Hall.

The book discusses research methodologies in the Communication field. It focuses on how case studies bridge the gap between communication research, theory, and practice.

Gilbert, V. K. (1981). The Case Study as a Research Methodology: Difficulties and Advantages of Integrating the Positivistic, Phenomenological and Grounded Theory Approaches . The Annual Meeting of the Canadian Association for the Study of Educational Administration. (Address) Halifax, NS, Can.

This study on an innovative secondary school in England shows how a "low-profile" participant-observer case study was crucial to the initial observation, the testing of hypotheses, the interpretive approach, and the grounded theory.

Gilgun, J. F. (1994). A Case for Case Studies in Social Work Research. Social Work, 39, 4, 371-381.

This article defines case study research, presents guidelines for evaluation of case studies, and shows the relevance of case studies to social work research. It also looks at issues such as evaluation and interpretations of case studies.

Glennan, S. L., Sharp-Bittner, M. A. & Tullos, D. C. (1991). Augmentative and Alternative Communication Training with a Nonspeaking Adult: Lessons from MH. Augmentative and Alternative Communication, 7, 240-7.

"A response-guided case study documented changes in a nonspeaking 36-yr-old man's ability to communicate using 3 trained augmentative communication modes. . . . Data were collected in videotaped interaction sessions between the nonspeaking adult and a series of adult speaking."

Graves, D. (1981). An Examination of the Writing Processes of Seven Year Old Children. Research in the Teaching of English, 15, 113-134.

Hamel, J. (1993). Case Study Methods . Newbury Park: Sage. .

"In a most economical fashion, Hamel provides a practical guide for producing theoretically sharp and empirically sound sociological case studies. A central idea put forth by Hamel is that case studies must "locate the global in the local" thus making the careful selection of the research site the most critical decision in the analytic process."

Karthigesu, R. (1986, July). Television as a Tool for Nation-Building in the Third World: A Post-Colonial Pattern, Using Malaysia as a Case-Study. International Television Studies Conference. (Address). London, 10-12.

"The extent to which Television Malaysia, as a national mass media organization, has been able to play a role in nation building in the post-colonial period is . . . studied in two parts: how the choice of a model of nation building determines the character of the organization; and how the character of the organization influences the output of the organization."

Kenny, R. (1984). Making the Case for the Case Study. Journal of Curriculum Studies, 16, (1), 37-51.

The article looks at how and why the case study is justified as a viable and valuable approach to educational research and program evaluation.

Knirk, F. (1991). Case Materials: Research and Practice. Performance Improvement Quarterly, 4 (1 ), 73-81.

The article addresses the effectiveness of case studies, subject areas where case studies are commonly used, recent examples of their use, and case study design considerations.

Klos, D. (1976). Students as Case Writers. Teaching of Psychology, 3.2, 63-66.

This article reviews a course in which students gather data for an original case study of another person. The task requires the students to design the study, collect the data, write the narrative, and interpret the findings.

Leftwich, A. (1981). The Politics of Case Study: Problems of Innovation in University Education. Higher Education Review, 13.2, 38-64.

The article discusses the use of case studies as a teaching method. Emphasis is on the instructional materials, interdisciplinarity, and the complex relationships within the university that help or hinder the method.

Mabrito, M. (1991, Oct.). Electronic Mail as a Vehicle for Peer Response: Conversations of High and Low Apprehensive Writers. Written Communication, 509-32.

McCarthy, S., J. (1955). The Influence of Classroom Discourse on Student Texts: The Case of Ella . East Lansing: Institute for Research on Teaching.

A look at how students of color become marginalized within traditional classroom discourse. The essay follows the struggles of one black student: Ella.

Matsuhashi, A., ed. (1987). Writing in Real Time: Modeling Production Processes Norwood, NJ: Ablex Publishing Corporation.

Investigates how writers plan to produce discourse for different purposes to report, to generalize, and to persuade, as well as how writers plan for sentence level units of language. To learn about planning, an observational measure of pause time was used" (ERIC).

Merriam, S. B. (1985). The Case Study in Educational Research: A Review of Selected Literature. Journal of Educational Thought, 19.3, 204-17.

The article examines the characteristics of, philosophical assumptions underlying the case study, the mechanics of conducting a case study, and the concerns about the reliability, validity, and generalizability of the method.

---. (1988). Case Study Research in Education: A Qualitative Approach San Francisco: Jossey Bass.

Merry, S. E., & Milner, N. eds. (1993). The Possibility of Popular Justice: A Case Study of Community Mediation in the United States . Ann Arbor: U of Michigan.

". . . this volume presents a case study of one experiment in popular justice, the San Francisco Community Boards. This program has made an explicit claim to create an alternative justice, or new justice, in the midst of a society ordered by state law. The contributors to this volume explore the history and experience of the program and compare it to other versions of popular justice in the United States, Europe, and the Third World."

Merseth, K. K. (1991). The Case for Cases in Teacher Education. RIE. 42p. (ERIC).

This monograph argues that the case method of instruction offers unique potential for revitalizing the field of teacher education.

Michaels, S. (1987). Text and Context: A New Approach to the Study of Classroom Writing. Discourse Processes, 10, 321-346.

"This paper argues for and illustrates an approach to the study of writing that integrates ethnographic analysis of classroom interaction with linguistic analysis of written texts and teacher/student conversational exchanges. The approach is illustrated through a case study of writing in a single sixth grade classroom during a single writing assignment."

Milburn, G. (1995). Deciphering a Code or Unraveling a Riddle: A Case Study in the Application of a Humanistic Metaphor to the Reporting of Social Studies Teaching. Theory and Research in Education, 13.

This citation serves as an example of how case studies document learning procedures in a senior-level economics course.

Milley, J. E. (1979). An Investigation of Case Study as an Approach to Program Evaluation. 19th Annual Forum of the Association for Institutional Research. (Address). San Diego.

The case study method merged a narrative report focusing on the evaluator as participant-observer with document review, interview, content analysis, attitude questionnaire survey, and sociogram analysis. Milley argues that case study program evaluation has great potential for widespread use.

Minnis, J. R. (1985, Sept.). Ethnography, Case Study, Grounded Theory, and Distance Education Research. Distance Education, 6.2.

This article describes and defines the strengths and weaknesses of ethnography, case study, and grounded theory.

Nunan, D. (1992). Collaborative language learning and teaching . New York: Cambridge University Press.

Included in this series of essays is Peter Sturman’s "Team Teaching: a case study from Japan" and David Nunan’s own "Toward a collaborative approach to curriculum development: a case study."

Nystrand, M., ed. (1982). What Writers Know: The Language, Process, and Structure of Written Discourse . New York: Academic Press.

Owenby, P. H. (1992). Making Case Studies Come Alive. Training, 29, (1), 43-46. (ERIC)

This article provides tips for writing more effective case studies.

---. (1981). Pausing and Planning: The Tempo of Writer Discourse Production. Research in the Teaching of English, 15 (2),113-34.

Perl, S. (1979). The Composing Processes of Unskilled College Writers. Research in the Teaching of English, 13, 317-336.

"Summarizes a study of five unskilled college writers, focusing especially on one of the five, and discusses the findings in light of current pedagogical practice and research design."

Pilcher J. and A. Coffey. eds. (1996). Gender and Qualitative Research . Brookfield: Aldershot, Hants, England.

This book provides a series of essays which look at gender identity research, qualitative research and applications of case study to questions of gendered pedagogy.

Pirie, B. S. (1993). The Case of Morty: A Four Year Study. Gifted Education International, 9 (2), 105-109.

This case study describes a boy from kindergarten through third grade with above average intelligence but difficulty in learning to read, write, and spell.

Popkewitz, T. (1993). Changing Patterns of Power: Social Regulation and Teacher Education Reform. Albany: SUNY Press.

Popkewitz edits this series of essays that address case studies on educational change and the training of teachers. The essays vary in terms of discipline and scope. Also, several authors include case studies of educational practices in countries other than the United States.

---. (1984). The Predrafting Processes of Four High- and Four Low Apprehensive Writers. Research in the Teaching of English, 18, (1), 45-64.

Rasmussen, P. (1985, March) A Case Study on the Evaluation of Research at the Technical University of Denmark. International Journal of Institutional Management in Higher Education, 9 (1).

This is an example of a case study methodology used to evaluate the chemistry and chemical engineering departments at the University of Denmark.

Roth, K. J. (1986). Curriculum Materials, Teacher Talk, and Student Learning: Case Studies in Fifth-Grade Science Teaching . East Lansing: Institute for Research on Teaching.

Roth offers case studies on elementary teachers, elementary school teaching, science studies and teaching, and verbal learning.

Selfe, C. L. (1985). An Apprehensive Writer Composes. When a Writer Can't Write: Studies in Writer's Block and Other Composing-Process Problems . (pp. 83-95). Ed. Mike Rose. NMY: Guilford.

Smith-Lewis, M., R. and Ford, A. (1987). A User's Perspective on Augmentative Communication. Augmentative and Alternative Communication, 3, 12-7.

"During a series of in-depth interviews, a 25-yr-old woman with cerebral palsy who utilized augmentative communication reflected on the effectiveness of the devices designed for her during her school career."

St. Pierre, R., G. (1980, April). Follow Through: A Case Study in Metaevaluation Research . 64th Annual Meeting of the American Educational Research Association. (Address).

The three approaches to metaevaluation are evaluation of primary evaluations, integrative meta-analysis with combined primary evaluation results, and re-analysis of the raw data from a primary evaluation.

Stahler, T., M. (1996, Feb.) Early Field Experiences: A Model That Worked. ERIC.

"This case study of a field and theory class examines a model designed to provide meaningful field experiences for preservice teachers while remaining consistent with the instructor's beliefs about the role of teacher education in preparing teachers for the classroom."

Stake, R. E. (1995). The Art of Case Study Research. Thousand Oaks: Sage Publications.

This book examines case study research in education and case study methodology.

Stiegelbauer, S. (1984) Community, Context, and Co-curriculum: Situational Factors Influencing School Improvements in a Study of High Schools. Presented at the annual meeting of the American Educational Research Association, New Orleans, LA.

Discussion of several case studies: one looking at high school environments, another examining educational innovations.

Stolovitch, H. (1990). Case Study Method. Performance And Instruction, 29, (9), 35-37.

This article describes the case study method as a form of simulation and presents guidelines for their use in professional training situations.

Thaller, E. (1994). Bibliography for the Case Method: Using Case Studies in Teacher Education. RIE. 37 p.

This bibliography presents approximately 450 citations on the use of case studies in teacher education from 1921-1993.

Thrane, T. (1986). On Delimiting the Senses of Near-Synonyms in Historical Semantics: A Case Study of Adjectives of 'Moral Sufficiency' in the Old English Andreas. Linguistics Across Historical and Geographical Boundaries: In Honor of Jacek Fisiak on the Occasion of his Fiftieth Birthday . Berlin: Mouton de Gruyter.

United Nations. (1975). Food and Agriculture Organization. Report on the FAO/UNFPA Seminar on Methodology, Research and Country: Case Studies on Population, Employment and Productivity . Rome: United Nations.

This example case study shows how the methodology can be used in a demographic and psychographic evaluation. At the same time, it discusses the formation and instigation of the case study methodology itself.

Van Vugt, J. P., ed. (1994). Aids Prevention and Services: Community Based Research . Westport: Bergin and Garvey.

"This volume has been five years in the making. In the process, some of the policy applications called for have met with limited success, such as free needle exchange programs in a limited number of American cities, providing condoms to prison inmates, and advertisements that depict same-sex couples. Rather than dating our chapters that deal with such subjects, such policy applications are verifications of the type of research demonstrated here. Furthermore, they indicate the critical need to continue community based research in the various communities threatened by acquired immuno-deficiency syndrome (AIDS) . . . "

Welch, W., ed. (1981, May). Case Study Methodology in Educational Evaluation. Proceedings of the Minnesota Evaluation Conference. Minnesota. (Address).

The four papers in these proceedings provide a comprehensive picture of the rationale, methodology, strengths, and limitations of case studies.

Williams, G. (1987). The Case Method: An Approach to Teaching and Learning in Educational Administration. RIE, 31p.

This paper examines the viability of the case method as a teaching and learning strategy in instructional systems geared toward the training of personnel of the administration of various aspects of educational systems.

Yin, R. K. (1993). Advancing Rigorous Methodologies: A Review of 'Towards Rigor in Reviews of Multivocal Literatures.' Review of Educational Research, 61, (3).

"R. T. Ogawa and B. Malen's article does not meet its own recommended standards for rigorous testing and presentation of its own conclusions. Use of the exploratory case study to analyze multivocal literatures is not supported, and the claim of grounded theory to analyze multivocal literatures may be stronger."

---. (1989). Case Study Research: Design and Methods. London: Sage Publications Inc.

This book discusses in great detail, the entire design process of the case study, including entire chapters on collecting evidence, analyzing evidence, composing the case study report, and designing single and multiple case studies.

Related Links

Consider the following list of related Web sites for more information on the topic of case study research. Note: although many of the links cover the general category of qualitative research, all have sections that address issues of case studies.

• Sage Publications on Qualitative Methodology: Search here for a comprehensive list of new books being published about "Qualitative Methodology" http://www.sagepub.co.uk/
• The International Journal of Qualitative Studies in Education: An on-line journal "to enhance the theory and practice of qualitative research in education." On-line submissions are welcome. http://www.tandf.co.uk/journals/tf/09518398.html
• Qualitative Research Resources on the Internet: From syllabi to home pages to bibliographies. All links relate somehow to qualitative research. http://www.nova.edu/ssss/QR/qualres.html

Becker, Bronwyn, Patrick Dawson, Karen Devine, Carla Hannum, Steve Hill, Jon Leydens, Debbie Matuskevich, Carol Traver, & Mike Palmquist. (2005). Case Studies. Writing@CSU . Colorado State University. https://writing.colostate.edu/guides/guide.cfm?guideid=60

Case Study Research and Applications

Design and methods.

Case Study Research

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Winner of the 2019 McGuffey Longevity Award from the Textbook & Academic Authors Association (TAA)

Recognized as one of the most cited methodology books in the social sciences, the Sixth Edition of Robert K. Yin's bestselling text provides a complete portal to the world of case study research. With the integration of 11 applications in this edition, the book gives readers access to exemplary case studies drawn from a wide variety of academic and applied fields. Ultimately, Case Study Research and Applications will guide students in the successful use and application of the case study research method.

Available formats

Chapter 1. getting started: how to know whether and when to use the case study as a research method, chapter 2. designing case studies: identifying your case(s) and establishing the logic of your case study, chapter 3. preparing to collect case study evidence: what you need to do before starting to collect case study data, chapter 4. collecting case study evidence: the principles you should follow in working with six sources of evidence, chapter 5. analyzing case study evidence: how to start your analysis, your analytic choices, and how they work, chapter 6. reporting case studies: how and what to compose.

Password-protected Instructor Resources include the following:

• An expanded glossary provided by the author in the form of downloadable Briefs.
• Additional tutorials written by the author which correspond to Chapters 1, 2, 3, 5, and 6.
• A selection of author Robert Yin's SAGE journal articles.
• Tables and figures from the book available for download.

Student Resource Site The open-access Student Study Site includes a selection of author Robert Yin's SAGE journal articles.

NEW TO THIS EDITION:

• Includes 11 in-depth applications that show how researchers have implemented case study methods successfully.
• Increases reference to relativist and constructivist approaches to case study research, as well as how case studies can be part of mixed methods projects.
• Places greater emphasis on using plausible rival explanations to bolster case study quality.
• Discusses synthesizing findings across case studies in a multiple-case study in more detail.
• Adds an expanded list of 15 fields that have text or texts devoted to case study research.
• Sharpens discussion of distinguishing research from non-research case studies.
• The author brings to light at least three remaining gaps to be filled in the future:
• how rival explanations can become more routinely integrated into all case study research;
• the difference between case-based and variable-based approaches to designing and analyzing case studies; and
• the relationship between case study research and qualitative research.

KEY FEATURES:

• Numerous conceptual exercises, illustrative exhibits, vignettes, and a glossary make the book eminently accessible.
• Boxes throughout offer more in-depth real-world examples of research.
• Short, sidebar tips help succinctly explain concepts and allow students to check their understanding.
• Exercises throughout offer students the chance to immediately apply their knowledge.

“The book is filled with tips to the researcher on how to master the craft of doing research overall and specifically how to account for multi-layered cases.” Asta Zelenkauskaite Drexel University

“Yin covers all of the basic and advanced knowledge for conducting case study and why they are useful for specific research studies without getting lost in the weeds.” Michael A Guerra Lincoln University

“The applications enhance the original material because it gives the reader concrete examples.” Claretha Hughes University of Arkansas

“Yin is much more in-depth on case study methods both within a general qualitative text and any other case study text I have seen.” David M. Sprick, PhD Park University

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Case study research and applications : design and methods

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• Foreword / Donald T. Campbell
• Getting started : how to know whether and when to use the case study as a research method
• Designing case studies : identifying your case(s) and establishing the logic of your case study
• Preparing to collect case study evidence : what you need to do before starting to collect case study data
• Collecting case study evidence : the principles you should follow in working with six sources of evidence
• Analyzing case study evidence : how to start your analysis, your analytic choices, and how they work
• Reporting case studies : how and what to compose.

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Applications of Case Study Research

This book by Robert K. Yin aims to help researchers and graduate level students to improve their knowledge and skills in conducting case study research. 21 individual applications of case study research are included that allow readers to see how the theory can be applied in practice. The book also includes sections on case study evaluations, as well as classroom activities. 

Chapter One of this book is available for free download from SAGE Publications. 

“ A. CASE STUDIES AS A RESEARCH (NOT TEACHING) METHOD

An Abbreviated Definition

All case study research starts from the same compelling feature: the desire to derive a(n) (up-)close or otherwise in-depth understanding of a single or small number of “cases,” set in their real-world contexts (e.g., Bromley, 1986, p. 1). The closeness aims to produce an invaluable and deep understanding—that is, an insightful appreciation of the “case(s)”—hopefully resulting in new learning about real-world behavior and its meaning. The distinctiveness of the case study, therefore, also serves as its abbreviated definition:

An empirical inquiry about a contemporary phenomenon (e.g., a “case”), set within its real-world context—especially when the boundaries between phenomenon and context are not clearly evident (Yin, 2009a, p. 18) .

Thus, among other features, case study research assumes that examining the context and other complex conditions related to the case(s) being studied are integral to understanding the case(s).

The in-depth focus on the case(s), as well as the desire to cover a broader range of contextual and other complex conditions, produce a wide range of topics to be covered by any given case study. In this sense, case study research goes beyond the study of isolated variables. As a by-product, and as a final feature in appreciating case study research, the relevant case study data are likely to come from multiple and not singular sources of evidence.” (Yin 2012, p.4)

• Chapter 1. A (Very) Brief Refresher on the Case Study Method
• Chapter 2. Field Notes
• Chapter 3. The Role of Theory in Doing Case Studies
• Chapter 4. Start-Up for a Newly-Appointed Education Leader
• Chapter 5. Citizens on Patrol
• Chapter 6. A Case Study of a Neighborhood Organization
• Chapter 7. A Nutshell Example: The Effect of a Federal Award on a University Computer Science Department
• Chapter 8. Essential Ingredients of Explanatory Case Studies: Three Drug Prevention Examples
• Chapter 9. Transforming a Business Firm Through Strategic Planning
• Chapter 10. Rival Explanations
• Chapter 11. Proposal Processing by Public and Private Universities
• Chapter 12. Case Studies of Transformed Firms
• PART V: Case Study Evaluations
• Chapter 13: Evaluation of a Community Coalition
• Chapter 14. Sheriff’s Combined Auto Theft Task Force
• Chapter 15. Technical Assistance for HIV/AIDS Community Planning

Yin, R. (2012).  Applications of Case Study Research . (Third ed.). SAGE Publications.

Related links

• http://www.uk.sagepub.com/books/Book235140/title

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Blog Business How to Present a Case Study like a Pro (With Examples)

How to Present a Case Study like a Pro (With Examples)

Written by: Danesh Ramuthi Sep 07, 2023

Okay, let’s get real: case studies can be kinda snooze-worthy. But guess what? They don’t have to be!

In this article, I will cover every element that transforms a mere report into a compelling case study, from selecting the right metrics to using persuasive narrative techniques.

And if you’re feeling a little lost, don’t worry! There are cool tools like Venngage’s Case Study Creator to help you whip up something awesome, even if you’re short on time. Plus, the pre-designed case study templates are like instant polish because let’s be honest, everyone loves a shortcut.

Click to jump ahead: 

What is a case study presentation?

What is the purpose of presenting a case study, how to structure a case study presentation, how long should a case study presentation be, 5 case study presentation examples with templates, 6 tips for delivering an effective case study presentation, 5 common mistakes to avoid in a case study presentation, how to present a case study faqs.

A case study presentation involves a comprehensive examination of a specific subject, which could range from an individual, group, location, event, organization or phenomenon.

They’re like puzzles you get to solve with the audience, all while making you think outside the box.

Unlike a basic report or whitepaper, the purpose of a case study presentation is to stimulate critical thinking among the viewers. 

The primary objective of a case study is to provide an extensive and profound comprehension of the chosen topic. You don’t just throw numbers at your audience. You use examples and real-life cases to make you think and see things from different angles.

The primary purpose of presenting a case study is to offer a comprehensive, evidence-based argument that informs, persuades and engages your audience.

Here’s the juicy part: presenting that case study can be your secret weapon. Whether you’re pitching a groundbreaking idea to a room full of suits or trying to impress your professor with your A-game, a well-crafted case study can be the magic dust that sprinkles brilliance over your words.

Think of it like digging into a puzzle you can’t quite crack . A case study lets you explore every piece, turn it over and see how it fits together. This close-up look helps you understand the whole picture, not just a blurry snapshot.

It’s also your chance to showcase how you analyze things, step by step, until you reach a conclusion. It’s all about being open and honest about how you got there.

Besides, presenting a case study gives you an opportunity to connect data and real-world scenarios in a compelling narrative. It helps to make your argument more relatable and accessible, increasing its impact on your audience.

One of the contexts where case studies can be very helpful is during the job interview. In some job interviews, you as candidates may be asked to present a case study as part of the selection process.

Having a case study presentation prepared allows the candidate to demonstrate their ability to understand complex issues, formulate strategies and communicate their ideas effectively.

The way you present a case study can make all the difference in how it’s received. A well-structured presentation not only holds the attention of your audience but also ensures that your key points are communicated clearly and effectively.

In this section, let’s go through the key steps that’ll help you structure your case study presentation for maximum impact.

Let’s get into it. 

Open with an introductory overview 

Start by introducing the subject of your case study and its relevance. Explain why this case study is important and who would benefit from the insights gained. This is your opportunity to grab your audience’s attention.

Explain the problem in question

Dive into the problem or challenge that the case study focuses on. Provide enough background information for the audience to understand the issue. If possible, quantify the problem using data or metrics to show the magnitude or severity.

Detail the solutions to solve the problem

After outlining the problem, describe the steps taken to find a solution. This could include the methodology, any experiments or tests performed and the options that were considered. Make sure to elaborate on why the final solution was chosen over the others.

Key stakeholders Involved

Talk about the individuals, groups or organizations that were directly impacted by or involved in the problem and its solution. 

Stakeholders may experience a range of outcomes—some may benefit, while others could face setbacks.

For example, in a business transformation case study, employees could face job relocations or changes in work culture, while shareholders might be looking at potential gains or losses.

Discuss the key results & outcomes

Discuss the results of implementing the solution. Use data and metrics to back up your statements. Did the solution meet its objectives? What impact did it have on the stakeholders? Be honest about any setbacks or areas for improvement as well.

Include visuals to support your analysis

Visual aids can be incredibly effective in helping your audience grasp complex issues. Utilize charts, graphs, images or video clips to supplement your points. Make sure to explain each visual and how it contributes to your overall argument.

Pie charts illustrate the proportion of different components within a whole, useful for visualizing market share, budget allocation or user demographics.

This is particularly useful especially if you’re displaying survey results in your case study presentation.

Stacked charts on the other hand are perfect for visualizing composition and trends. This is great for analyzing things like customer demographics, product breakdowns or budget allocation in your case study.

Consider this example of a stacked bar chart template. It provides a straightforward summary of the top-selling cake flavors across various locations, offering a quick and comprehensive view of the data.

Not the chart you’re looking for? Browse Venngage’s gallery of chart templates to find the perfect one that’ll captivate your audience and level up your data storytelling.

Recommendations and next steps

Wrap up by providing recommendations based on the case study findings. Outline the next steps that stakeholders should take to either expand on the success of the project or address any remaining challenges.

Acknowledgments and references

Thank the people who contributed to the case study and helped in the problem-solving process. Cite any external resources, reports or data sets that contributed to your analysis.

Feedback & Q&A session

Open the floor for questions and feedback from your audience. This allows for further discussion and can provide additional insights that may not have been considered previously.

Closing remarks

Conclude the presentation by summarizing the key points and emphasizing the takeaways. Thank your audience for their time and participation and express your willingness to engage in further discussions or collaborations on the subject.

Well, the length of a case study presentation can vary depending on the complexity of the topic and the needs of your audience. However, a typical business or academic presentation often lasts between 15 to 30 minutes. 

This time frame usually allows for a thorough explanation of the case while maintaining audience engagement. However, always consider leaving a few minutes at the end for a Q&A session to address any questions or clarify points made during the presentation.

When it comes to presenting a compelling case study, having a well-structured template can be a game-changer. 

It helps you organize your thoughts, data and findings in a coherent and visually pleasing manner. 

Not all case studies are created equal and different scenarios require distinct approaches for maximum impact. 

To save you time and effort, I have curated a list of 5 versatile case study presentation templates, each designed for specific needs and audiences. 

Here are some best case study presentation examples that showcase effective strategies for engaging your audience and conveying complex information clearly.

1 . Lab report case study template

Ever feel like your research gets lost in a world of endless numbers and jargon? Lab case studies are your way out!

Think of it as building a bridge between your cool experiment and everyone else. It’s more than just reporting results – it’s explaining the “why” and “how” in a way that grabs attention and makes sense.

This lap report template acts as a blueprint for your report, guiding you through each essential section (introduction, methods, results, etc.) in a logical order.

Want to present your research like a pro? Browse our research presentation template gallery for creative inspiration!

2. Product case study template

It’s time you ditch those boring slideshows and bullet points because I’ve got a better way to win over clients: product case study templates.

Instead of just listing features and benefits, you get to create a clear and concise story that shows potential clients exactly what your product can do for them. It’s like painting a picture they can easily visualize, helping them understand the value your product brings to the table.

Grab the template below, fill in the details, and watch as your product’s impact comes to life!

3. Content marketing case study template

In digital marketing, showcasing your accomplishments is as vital as achieving them. 

A well-crafted case study not only acts as a testament to your successes but can also serve as an instructional tool for others. 

With this coral content marketing case study template—a perfect blend of vibrant design and structured documentation, you can narrate your marketing triumphs effectively.

4. Case study psychology template

Understanding how people tick is one of psychology’s biggest quests and case studies are like magnifying glasses for the mind. They offer in-depth looks at real-life behaviors, emotions and thought processes, revealing fascinating insights into what makes us human.

Writing a top-notch case study, though, can be a challenge. It requires careful organization, clear presentation and meticulous attention to detail. That’s where a good case study psychology template comes in handy.

Think of it as a helpful guide, taking care of formatting and structure while you focus on the juicy content. No more wrestling with layouts or margins – just pour your research magic into crafting a compelling narrative.

5. Lead generation case study template

Lead generation can be a real head-scratcher. But here’s a little help: a lead generation case study.

Think of it like a friendly handshake and a confident resume all rolled into one. It’s your chance to showcase your expertise, share real-world successes and offer valuable insights. Potential clients get to see your track record, understand your approach and decide if you’re the right fit.

No need to start from scratch, though. This lead generation case study template guides you step-by-step through crafting a clear, compelling narrative that highlights your wins and offers actionable tips for others. Fill in the gaps with your specific data and strategies, and voilà! You’ve got a powerful tool to attract new customers.

Related: 15+ Professional Case Study Examples [Design Tips + Templates]

So, you’ve spent hours crafting the perfect case study and are now tasked with presenting it. Crafting the case study is only half the battle; delivering it effectively is equally important. 

Whether you’re facing a room of executives, academics or potential clients, how you present your findings can make a significant difference in how your work is received. 

Forget boring reports and snooze-inducing presentations! Let’s make your case study sing. Here are some key pointers to turn information into an engaging and persuasive performance:

• Know your audience : Tailor your presentation to the knowledge level and interests of your audience. Remember to use language and examples that resonate with them.
• Rehearse : Rehearsing your case study presentation is the key to a smooth delivery and for ensuring that you stay within the allotted time. Practice helps you fine-tune your pacing, hone your speaking skills with good word pronunciations and become comfortable with the material, leading to a more confident, conversational and effective presentation.
• Start strong : Open with a compelling introduction that grabs your audience’s attention. You might want to use an interesting statistic, a provocative question or a brief story that sets the stage for your case study.
• Be clear and concise : Avoid jargon and overly complex sentences. Get to the point quickly and stay focused on your objectives.
• Use visual aids : Incorporate slides with graphics, charts or videos to supplement your verbal presentation. Make sure they are easy to read and understand.
• Tell a story : Use storytelling techniques to make the case study more engaging. A well-told narrative can help you make complex data more relatable and easier to digest.

Ditching the dry reports and slide decks? Venngage’s case study templates let you wow customers with your solutions and gain insights to improve your business plan. Pre-built templates, visual magic and customer captivation – all just a click away. Go tell your story and watch them say “wow!”

Nailed your case study, but want to make your presentation even stronger? Avoid these common mistakes to ensure your audience gets the most out of it:

Overloading with information

A case study is not an encyclopedia. Overloading your presentation with excessive data, text or jargon can make it cumbersome and difficult for the audience to digest the key points. Stick to what’s essential and impactful. Need help making your data clear and impactful? Our data presentation templates can help! Find clear and engaging visuals to showcase your findings.

Lack of structure

Jumping haphazardly between points or topics can confuse your audience. A well-structured presentation, with a logical flow from introduction to conclusion, is crucial for effective communication.

Ignoring the audience

Different audiences have different needs and levels of understanding. Failing to adapt your presentation to your audience can result in a disconnect and a less impactful presentation.

Poor visual elements

While content is king, poor design or lack of visual elements can make your case study dull or hard to follow. Make sure you use high-quality images, graphs and other visual aids to support your narrative.

Not focusing on results

A case study aims to showcase a problem and its solution, but what most people care about are the results. Failing to highlight or adequately explain the outcomes can make your presentation fall flat.

How to start a case study presentation?

Starting a case study presentation effectively involves a few key steps:

• Grab attention : Open with a hook—an intriguing statistic, a provocative question or a compelling visual—to engage your audience from the get-go.
• Set the stage : Briefly introduce the subject, context and relevance of the case study to give your audience an idea of what to expect.
• Outline objectives : Clearly state what the case study aims to achieve. Are you solving a problem, proving a point or showcasing a success?
• Agenda : Give a quick outline of the key sections or topics you’ll cover to help the audience follow along.
• Set expectations : Let your audience know what you want them to take away from the presentation, whether it’s knowledge, inspiration or a call to action.

How to present a case study on PowerPoint and on Google Slides?

Presenting a case study on PowerPoint and Google Slides involves a structured approach for clarity and impact using presentation slides :

• Title slide : Start with a title slide that includes the name of the case study, your name and any relevant institutional affiliations.
• Introduction : Follow with a slide that outlines the problem or situation your case study addresses. Include a hook to engage the audience.
• Objectives : Clearly state the goals of the case study in a dedicated slide.
• Findings : Use charts, graphs and bullet points to present your findings succinctly.
• Analysis : Discuss what the findings mean, drawing on supporting data or secondary research as necessary.
• Conclusion : Summarize key takeaways and results.
• Q&A : End with a slide inviting questions from the audience.

What’s the role of analysis in a case study presentation?

The role of analysis in a case study presentation is to interpret the data and findings, providing context and meaning to them. 

It helps your audience understand the implications of the case study, connects the dots between the problem and the solution and may offer recommendations for future action.

Is it important to include real data and results in the presentation?

Yes, including real data and results in a case study presentation is crucial to show experience,  credibility and impact. Authentic data lends weight to your findings and conclusions, enabling the audience to trust your analysis and take your recommendations more seriously

How do I conclude a case study presentation effectively?

To conclude a case study presentation effectively, summarize the key findings, insights and recommendations in a clear and concise manner. 

End with a strong call-to-action or a thought-provoking question to leave a lasting impression on your audience.

What’s the best way to showcase data in a case study presentation ?

The best way to showcase data in a case study presentation is through visual aids like charts, graphs and infographics which make complex information easily digestible, engaging and creative. 

Don’t just report results, visualize them! This template for example lets you transform your social media case study into a captivating infographic that sparks conversation.

Choose the type of visual that best represents the data you’re showing; for example, use bar charts for comparisons or pie charts for parts of a whole. 

Ensure that the visuals are high-quality and clearly labeled, so the audience can quickly grasp the key points. 

Keep the design consistent and simple, avoiding clutter or overly complex visuals that could distract from the message.

Choose a template that perfectly suits your case study where you can utilize different visual aids for maximum impact. 

Need more inspiration on how to turn numbers into impact with the help of infographics? Our ready-to-use infographic templates take the guesswork out of creating visual impact for your case studies with just a few clicks.

Related: 10+ Case Study Infographic Templates That Convert

Congrats on mastering the art of compelling case study presentations! This guide has equipped you with all the essentials, from structure and nuances to avoiding common pitfalls. You’re ready to impress any audience, whether in the boardroom, the classroom or beyond.

And remember, you’re not alone in this journey. Venngage’s Case Study Creator is your trusty companion, ready to elevate your presentations from ordinary to extraordinary. So, let your confidence shine, leverage your newly acquired skills and prepare to deliver presentations that truly resonate.

Go forth and make a lasting impact!

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Continuing to enhance the quality of case study methodology in health services research

Shannon l. sibbald.

1 Faculty of Health Sciences, Western University, London, Ontario, Canada.

2 Department of Family Medicine, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada.

3 The Schulich Interfaculty Program in Public Health, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada.

Stefan Paciocco

Meghan fournie, rachelle van asseldonk, tiffany scurr.

Case study methodology has grown in popularity within Health Services Research (HSR). However, its use and merit as a methodology are frequently criticized due to its flexible approach and inconsistent application. Nevertheless, case study methodology is well suited to HSR because it can track and examine complex relationships, contexts, and systems as they evolve. Applied appropriately, it can help generate information on how multiple forms of knowledge come together to inform decision-making within healthcare contexts. In this article, we aim to demystify case study methodology by outlining its philosophical underpinnings and three foundational approaches. We provide literature-based guidance to decision-makers, policy-makers, and health leaders on how to engage in and critically appraise case study design. We advocate that researchers work in collaboration with health leaders to detail their research process with an aim of strengthening the validity and integrity of case study for its continued and advanced use in HSR.

Introduction

The popularity of case study research methodology in Health Services Research (HSR) has grown over the past 40 years. 1 This may be attributed to a shift towards the use of implementation research and a newfound appreciation of contextual factors affecting the uptake of evidence-based interventions within diverse settings. 2 Incorporating context-specific information on the delivery and implementation of programs can increase the likelihood of success. 3 , 4 Case study methodology is particularly well suited for implementation research in health services because it can provide insight into the nuances of diverse contexts. 5 , 6 In 1999, Yin 7 published a paper on how to enhance the quality of case study in HSR, which was foundational for the emergence of case study in this field. Yin 7 maintains case study is an appropriate methodology in HSR because health systems are constantly evolving, and the multiple affiliations and diverse motivations are difficult to track and understand with traditional linear methodologies.

Despite its increased popularity, there is debate whether a case study is a methodology (ie, a principle or process that guides research) or a method (ie, a tool to answer research questions). Some criticize case study for its high level of flexibility, perceiving it as less rigorous, and maintain that it generates inadequate results. 8 Others have noted issues with quality and consistency in how case studies are conducted and reported. 9 Reporting is often varied and inconsistent, using a mix of approaches such as case reports, case findings, and/or case study. Authors sometimes use incongruent methods of data collection and analysis or use the case study as a default when other methodologies do not fit. 9 , 10 Despite these criticisms, case study methodology is becoming more common as a viable approach for HSR. 11 An abundance of articles and textbooks are available to guide researchers through case study research, including field-specific resources for business, 12 , 13 nursing, 14 and family medicine. 15 However, there remains confusion and a lack of clarity on the key tenets of case study methodology.

Several common philosophical underpinnings have contributed to the development of case study research 1 which has led to different approaches to planning, data collection, and analysis. This presents challenges in assessing quality and rigour for researchers conducting case studies and stakeholders reading results.

This article discusses the various approaches and philosophical underpinnings to case study methodology. Our goal is to explain it in a way that provides guidance for decision-makers, policy-makers, and health leaders on how to understand, critically appraise, and engage in case study research and design, as such guidance is largely absent in the literature. This article is by no means exhaustive or authoritative. Instead, we aim to provide guidance and encourage dialogue around case study methodology, facilitating critical thinking around the variety of approaches and ways quality and rigour can be bolstered for its use within HSR.

Purpose of case study methodology

Case study methodology is often used to develop an in-depth, holistic understanding of a specific phenomenon within a specified context. 11 It focuses on studying one or multiple cases over time and uses an in-depth analysis of multiple information sources. 16 , 17 It is ideal for situations including, but not limited to, exploring under-researched and real-life phenomena, 18 especially when the contexts are complex and the researcher has little control over the phenomena. 19 , 20 Case studies can be useful when researchers want to understand how interventions are implemented in different contexts, and how context shapes the phenomenon of interest.

In addition to demonstrating coherency with the type of questions case study is suited to answer, there are four key tenets to case study methodologies: (1) be transparent in the paradigmatic and theoretical perspectives influencing study design; (2) clearly define the case and phenomenon of interest; (3) clearly define and justify the type of case study design; and (4) use multiple data collection sources and analysis methods to present the findings in ways that are consistent with the methodology and the study’s paradigmatic base. 9 , 16 The goal is to appropriately match the methods to empirical questions and issues and not to universally advocate any single approach for all problems. 21

Approaches to case study methodology

Three authors propose distinct foundational approaches to case study methodology positioned within different paradigms: Yin, 19 , 22 Stake, 5 , 23 and Merriam 24 , 25 ( Table 1 ). Yin is strongly post-positivist whereas Stake and Merriam are grounded in a constructivist paradigm. Researchers should locate their research within a paradigm that explains the philosophies guiding their research 26 and adhere to the underlying paradigmatic assumptions and key tenets of the appropriate author’s methodology. This will enhance the consistency and coherency of the methods and findings. However, researchers often do not report their paradigmatic position, nor do they adhere to one approach. 9 Although deliberately blending methodologies may be defensible and methodologically appropriate, more often it is done in an ad hoc and haphazard way, without consideration for limitations.

Cross-analysis of three case study approaches, adapted from Yazan 2015

The post-positive paradigm postulates there is one reality that can be objectively described and understood by “bracketing” oneself from the research to remove prejudice or bias. 27 Yin focuses on general explanation and prediction, emphasizing the formulation of propositions, akin to hypothesis testing. This approach is best suited for structured and objective data collection 9 , 11 and is often used for mixed-method studies.

Constructivism assumes that the phenomenon of interest is constructed and influenced by local contexts, including the interaction between researchers, individuals, and their environment. 27 It acknowledges multiple interpretations of reality 24 constructed within the context by the researcher and participants which are unlikely to be replicated, should either change. 5 , 20 Stake and Merriam’s constructivist approaches emphasize a story-like rendering of a problem and an iterative process of constructing the case study. 7 This stance values researcher reflexivity and transparency, 28 acknowledging how researchers’ experiences and disciplinary lenses influence their assumptions and beliefs about the nature of the phenomenon and development of the findings.

Defining a case

A key tenet of case study methodology often underemphasized in literature is the importance of defining the case and phenomenon. Researches should clearly describe the case with sufficient detail to allow readers to fully understand the setting and context and determine applicability. Trying to answer a question that is too broad often leads to an unclear definition of the case and phenomenon. 20 Cases should therefore be bound by time and place to ensure rigor and feasibility. 6

Yin 22 defines a case as “a contemporary phenomenon within its real-life context,” (p13) which may contain a single unit of analysis, including individuals, programs, corporations, or clinics 29 (holistic), or be broken into sub-units of analysis, such as projects, meetings, roles, or locations within the case (embedded). 30 Merriam 24 and Stake 5 similarly define a case as a single unit studied within a bounded system. Stake 5 , 23 suggests bounding cases by contexts and experiences where the phenomenon of interest can be a program, process, or experience. However, the line between the case and phenomenon can become muddy. For guidance, Stake 5 , 23 describes the case as the noun or entity and the phenomenon of interest as the verb, functioning, or activity of the case.

Designing the case study approach

Yin’s approach to a case study is rooted in a formal proposition or theory which guides the case and is used to test the outcome. 1 Stake 5 advocates for a flexible design and explicitly states that data collection and analysis may commence at any point. Merriam’s 24 approach blends both Yin and Stake’s, allowing the necessary flexibility in data collection and analysis to meet the needs.

Yin 30 proposed three types of case study approaches—descriptive, explanatory, and exploratory. Each can be designed around single or multiple cases, creating six basic case study methodologies. Descriptive studies provide a rich description of the phenomenon within its context, which can be helpful in developing theories. To test a theory or determine cause and effect relationships, researchers can use an explanatory design. An exploratory model is typically used in the pilot-test phase to develop propositions (eg, Sibbald et al. 31 used this approach to explore interprofessional network complexity). Despite having distinct characteristics, the boundaries between case study types are flexible with significant overlap. 30 Each has five key components: (1) research question; (2) proposition; (3) unit of analysis; (4) logical linking that connects the theory with proposition; and (5) criteria for analyzing findings.

Contrary to Yin, Stake 5 believes the research process cannot be planned in its entirety because research evolves as it is performed. Consequently, researchers can adjust the design of their methods even after data collection has begun. Stake 5 classifies case studies into three categories: intrinsic, instrumental, and collective/multiple. Intrinsic case studies focus on gaining a better understanding of the case. These are often undertaken when the researcher has an interest in a specific case. Instrumental case study is used when the case itself is not of the utmost importance, and the issue or phenomenon (ie, the research question) being explored becomes the focus instead (eg, Paciocco 32 used an instrumental case study to evaluate the implementation of a chronic disease management program). 5 Collective designs are rooted in an instrumental case study and include multiple cases to gain an in-depth understanding of the complexity and particularity of a phenomenon across diverse contexts. 5 , 23 In collective designs, studying similarities and differences between the cases allows the phenomenon to be understood more intimately (for examples of this in the field, see van Zelm et al. 33 and Burrows et al. 34 In addition, Sibbald et al. 35 present an example where a cross-case analysis method is used to compare instrumental cases).

Merriam’s approach is flexible (similar to Stake) as well as stepwise and linear (similar to Yin). She advocates for conducting a literature review before designing the study to better understand the theoretical underpinnings. 24 , 25 Unlike Stake or Yin, Merriam proposes a step-by-step guide for researchers to design a case study. These steps include performing a literature review, creating a theoretical framework, identifying the problem, creating and refining the research question(s), and selecting a study sample that fits the question(s). 24 , 25 , 36

Data collection and analysis

Using multiple data collection methods is a key characteristic of all case study methodology; it enhances the credibility of the findings by allowing different facets and views of the phenomenon to be explored. 23 Common methods include interviews, focus groups, observation, and document analysis. 5 , 37 By seeking patterns within and across data sources, a thick description of the case can be generated to support a greater understanding and interpretation of the whole phenomenon. 5 , 17 , 20 , 23 This technique is called triangulation and is used to explore cases with greater accuracy. 5 Although Stake 5 maintains case study is most often used in qualitative research, Yin 17 supports a mix of both quantitative and qualitative methods to triangulate data. This deliberate convergence of data sources (or mixed methods) allows researchers to find greater depth in their analysis and develop converging lines of inquiry. For example, case studies evaluating interventions commonly use qualitative interviews to describe the implementation process, barriers, and facilitators paired with a quantitative survey of comparative outcomes and effectiveness. 33 , 38 , 39

Yin 30 describes analysis as dependent on the chosen approach, whether it be (1) deductive and rely on theoretical propositions; (2) inductive and analyze data from the “ground up”; (3) organized to create a case description; or (4) used to examine plausible rival explanations. According to Yin’s 40 approach to descriptive case studies, carefully considering theory development is an important part of study design. “Theory” refers to field-relevant propositions, commonly agreed upon assumptions, or fully developed theories. 40 Stake 5 advocates for using the researcher’s intuition and impression to guide analysis through a categorical aggregation and direct interpretation. Merriam 24 uses six different methods to guide the “process of making meaning” (p178) : (1) ethnographic analysis; (2) narrative analysis; (3) phenomenological analysis; (4) constant comparative method; (5) content analysis; and (6) analytic induction.

Drawing upon a theoretical or conceptual framework to inform analysis improves the quality of case study and avoids the risk of description without meaning. 18 Using Stake’s 5 approach, researchers rely on protocols and previous knowledge to help make sense of new ideas; theory can guide the research and assist researchers in understanding how new information fits into existing knowledge.

Practical applications of case study research

Columbia University has recently demonstrated how case studies can help train future health leaders. 41 Case studies encompass components of systems thinking—considering connections and interactions between components of a system, alongside the implications and consequences of those relationships—to equip health leaders with tools to tackle global health issues. 41 Greenwood 42 evaluated Indigenous peoples’ relationship with the healthcare system in British Columbia and used a case study to challenge and educate health leaders across the country to enhance culturally sensitive health service environments.

An important but often omitted step in case study research is an assessment of quality and rigour. We recommend using a framework or set of criteria to assess the rigour of the qualitative research. Suitable resources include Caelli et al., 43 Houghten et al., 44 Ravenek and Rudman, 45 and Tracy. 46

New directions in case study

Although “pragmatic” case studies (ie, utilizing practical and applicable methods) have existed within psychotherapy for some time, 47 , 48 only recently has the applicability of pragmatism as an underlying paradigmatic perspective been considered in HSR. 49 This is marked by uptake of pragmatism in Randomized Control Trials, recognizing that “gold standard” testing conditions do not reflect the reality of clinical settings 50 , 51 nor do a handful of epistemologically guided methodologies suit every research inquiry.

Pragmatism positions the research question as the basis for methodological choices, rather than a theory or epistemology, allowing researchers to pursue the most practical approach to understanding a problem or discovering an actionable solution. 52 Mixed methods are commonly used to create a deeper understanding of the case through converging qualitative and quantitative data. 52 Pragmatic case study is suited to HSR because its flexibility throughout the research process accommodates complexity, ever-changing systems, and disruptions to research plans. 49 , 50 Much like case study, pragmatism has been criticized for its flexibility and use when other approaches are seemingly ill-fit. 53 , 54 Similarly, authors argue that this results from a lack of investigation and proper application rather than a reflection of validity, legitimizing the need for more exploration and conversation among researchers and practitioners. 55

Although occasionally misunderstood as a less rigourous research methodology, 8 case study research is highly flexible and allows for contextual nuances. 5 , 6 Its use is valuable when the researcher desires a thorough understanding of a phenomenon or case bound by context. 11 If needed, multiple similar cases can be studied simultaneously, or one case within another. 16 , 17 There are currently three main approaches to case study, 5 , 17 , 24 each with their own definitions of a case, ontological and epistemological paradigms, methodologies, and data collection and analysis procedures. 37

Individuals’ experiences within health systems are influenced heavily by contextual factors, participant experience, and intricate relationships between different organizations and actors. 55 Case study research is well suited for HSR because it can track and examine these complex relationships and systems as they evolve over time. 6 , 7 It is important that researchers and health leaders using this methodology understand its key tenets and how to conduct a proper case study. Although there are many examples of case study in action, they are often under-reported and, when reported, not rigorously conducted. 9 Thus, decision-makers and health leaders should use these examples with caution. The proper reporting of case studies is necessary to bolster their credibility in HSR literature and provide readers sufficient information to critically assess the methodology. We also call on health leaders who frequently use case studies 56 – 58 to report them in the primary research literature.

The purpose of this article is to advocate for the continued and advanced use of case study in HSR and to provide literature-based guidance for decision-makers, policy-makers, and health leaders on how to engage in, read, and interpret findings from case study research. As health systems progress and evolve, the application of case study research will continue to increase as researchers and health leaders aim to capture the inherent complexities, nuances, and contextual factors. 7

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Application of a mobile health data platform for public health surveillance: A case study in stress monitoring and prediction

Affiliations.

• 1 School of Public Health Sciences, University of Waterloo, Waterloo, ON, Canada.
• 2 David R. Cheriton School of Computer Science, University of Waterloo, Waterloo, ON, Canada.
• 3 Research Institute for Aging, University of Waterloo, Waterloo, ON, Canada.
• 4 Department of Systems Design Engineering, University of Waterloo, Waterloo, ON, Canada.
• 5 Institute of Health Policy, Management, and Evaluation, Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada.
• 6 Centre for Digital Therapeutics, Techna Institute, University Health Network, Toronto, ON, Canada.
• PMID: 39281042
• PMCID: PMC11394344
• DOI: 10.1177/20552076241249931

Background: Public health surveillance involves the collection, analysis and dissemination of data to improve population health. The main sources of data for public health decision-making are surveys, typically comprised of self-report which may be subject to biases, costs and delays. To complement subjective data, objective measures from sensors could potentially be used. Specifically, advancements in personal mobile and wearable technologies enable the collection of real-time and continuous health data.

Objective: In this context, the goal of this work is to apply a mobile health platform (MHP) that extracts health data from the Apple Health repository to collect data in daily-life scenarios and use it for the prediction of stress, a major public health issue.

Methods: A pilot study was conducted with 45 participants over 2 weeks, using the MHP to collect stress-related data from Apple Health and perceived stress self-reports. Apple, Withings and Empatica devices were distributed to participants and collected a wide range of data, including heart rate, sleep, blood pressure, temperature, and weight. These were used to train random forests and support vector machines. The SMOTE technique was used to handle imbalanced datasets.

Results: Accuracy and f1-macro scores were in line with state-of-the-art models for stress prediction above 60% for the majority of analyses and samples analysed. Apple Watch sleep features were particularly good predictors, with most models with these data achieving results around 70%.

Conclusions: A system such as the MHP could be used for public health data collection, complementing traditional self-reporting methods when possible. The data collected with the system was promising for monitoring and predicting stress in a population.

Keywords: Apple Health; Public health; app; heart rate; mHealth; machine learning; sleep; stress.

© The Author(s) 2024.

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Study protocol.

MHP interface.

Division into datasets per device…

Division into datasets per device and per device + sleep.

Training generalised models.

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• Published: 18 September 2024

Susceptibility assessment of multi-hazards using random forest—back propagation neural network coupling model: a Hangzhou city case study

• Bofan Yu 1 , 2 ,
• Huaixue Xing 1 &
• Jiaxing Yan 2  

Scientific Reports volume  14 , Article number:  21783 ( 2024 ) Cite this article

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• Environmental impact
• Natural hazards

As the demand for regional geological disaster risk assessments in large cities continues to rise, our study selected Hangzhou, one of China’s megacities, as a model to evaluate the susceptibility to two major geological hazards in the region: ground collapse and ground subsidence. Given that susceptibility assessments for such disasters mainly rely on knowledge-driven models, and data-driven models have significant potential for application, we proposed a high-accuracy Random Forest—Back Propagation Neural Network Coupling Model. By using nine evaluation factors selected based on field surveys and expert recommendations, along with disaster data, the model's predictive results indicate a 3–40% improvement in model performance metrics such as AUC, accuracy, precision, recall, and F1-score, compared to single models and traditional SVM and logistic regression models. Ultimately, using the predictive results of this model, we created susceptibility maps for individual disasters and developed a muti-hazards susceptibility map by employing the expert weight discrimination method and the overlay evaluation method. Furthermore, we discussed the feature importance in the prediction process. Our study validated the feasibility of using advanced machine learning models for urban geological disaster assessment, providing a replicable template for other cities.

Introduction

With the continuous expansion of urban construction, the conflict between urban geological disasters and urban development has become increasingly prominent 1 , 2 . The prevention and management of geological disasters have thus become critical considerations for every city 3 . Hangzhou, one of China’s megacities, boasts a population exceeding 10 million and achieved a GDP of $259 billion in 2022 4 . However, due to its location in the Hangjiahu Plain and ongoing human-induced modifications to the geological environment 5 , 6 , issues like land subsidence and ground collapse in Hangzhou’s main urban areas have emerged as significant challenges during its development. Specifically, subsidence primarily results from extensive urban development and the prevalent distribution of Quaternary soft soil layers, which are susceptible to compression under structural loads. In contrast, collapses are mainly triggered by the presence of artificial fill and the failure of underground pipelines. Like many cities, Hangzhou has started to undertake regional geological disaster assessments to ensure urban geological safety. The assessment and prediction of these disasters necessitate susceptibility evaluation, as it reflects geological conditions and enables reasonable zoning of the study area 7 , 8 , 9 , 10 . However, assessments based solely on single disaster types might not accurately represent the geological safety of an area, especially as more cities begin to emphasize the overall impact of regional geological issues. Therefore, comprehensive evaluations encompassing multiple types of disasters, or multi-hazards, are commonly employed 11 , 12 , 13 . Current assessments, especially those concerning subsidence and collapse, primarily rely on knowledge-driven models such as the Analytic Hierarchy Process (AHP), which entails subjective scoring of selected indicators to determine their weights for susceptibility analysis 14 , 15 , 16 , Particularly for collapse-related disasters, which occur over small areas, machine learning-based susceptibility assessments of such disasters are, to our knowledge, currently an unexplored area. Meanwhile, in the context of comprehensive disaster evaluations, experts commonly employ AHP to score and determine weights 17 , 18 , 19 , when assessing the relative weights of different types of disasters within a specific area, the lack of learning samples means that reliance on expert judgment is the only viable option.

With advancements in technology and the growing complexity of geological disaster conditions, the limitations of the AHP are becoming increasingly apparent 20 . Its reliance on expert judgment for weighting factors is inherently subjective and can be influenced by factors such as emotions, fatigue, among others, particularly with numerous evaluation criteria. Consequently, researchers are increasingly turning to data-driven models. Unlike traditional models, data-driven models are capable of handling more complex datasets, thereby improving prediction accuracy. They have been extensively applied in evaluating susceptibility to large-scale geological disasters, such as landslides and earthquakes 21 , 22 , 23 , 24 , 25 . Recently, the integration of coupling machine learning models, such as the combination of BP neural networks with SVM models, has demonstrated potential in optimizing predictions by leveraging each model’s strengths and mitigating single-model flaws, thus achieving higher accuracy in case studies 26 , 27 . However, there is still significant potential for development in the field of ensemble models, particularly in urban geological disasters. When facing datasets that include complex geological environments and human activity factors, enhancing the predictive performance of models is crucial for the accuracy of prediction results.

Our study assesses the susceptibility of multi-hazards, including ground subsidence and ground collapse, in commonly filled and silty areas in Hangzhou by employing Random Forest - Back Propagation Neural Network coupling model. We explored the feasibility of utilizing coupled models over single models to enhance evaluation effectiveness, particularly providing a viable template for applying machine learning to small-scale, collapse-type disasters. Our research flowchart is illustrated in Fig. 1 .

Research flowchart.

Materials and methodology

Selection of the study area.

The silty clay soil in Hangzhou City is primarily distributed in the plain areas. Due to the topographic and geomorphological characteristics, the plain areas with accumulative, alluvial, and marine plains are the most typical regions. Considering the comprehensive disaster situation, this paper selects the filled soil-silty clay typical area along the south bank of the Qiantang River in Binjiang District as the study area. Covering an area of 31,970,000m 2 (31.97 km 2 ), it includes urban arterials such as subways, expressways, and elevated roads, marking it as a region in Hangzhou City with significant human activity modifications. The study area is located along the western edge of the Xiaoshao Plain, north to the Hangzhou duplex hill, and south to the Puyang River Plain. The terrain is dominated by plains with a few low hills, featuring monotonous geomorphological types with clear boundaries, flat terrain, a dense river network, and mainly consists of sandy silty soil and silt, with the sand and gravel layer buried at a depth of about 35–50 m. Human activities have profoundly affected the area, with high-rise buildings typically using sand-gravel layers or bedrock as the bearing stratum. The sediments mainly consist of gray to dark gray silty mud clay and silty fine clay, characterized by distinct horizontal stratification and high-water content. The Quaternary strata mainly belong to the lower part of the Holocene, formed during the early Fuyang marine transgression, primarily through flood alluviation, often appearing as river valley plains, river terraces, and other landforms. The strata are composed of sand and gravel, with good sorting and rounding, relatively loose structure, and a thickness of 2–12 m. The geographical location of the study area is shown in Fig. 2 .

Copyright © 2020 Esri and its licensors. All rights reserved. Esri, NASA, NGA, USGS, Sources: Esri, USGS, Esri, © OpenStreetMap contributors, TomTom, Garmin, FAO, NOAA, USGS.)

Location of the study area (This figure was created using ArcGIS Pro software. Desktop GIS Software | Mapping Analytics | ArcGIS Pro (esri.com)) (Map image is the intellectual property of Esri and is used herein under license.

Selection of evaluation factors

Considering the complexity of the urban geological environment and the unique characteristics of the study area, it is imperative to select evaluation factors that comprehensively consider the intensity of human activities in the area and conduct in-depth analyses in conjunction with geological conditions and cultural characteristics. To determine which influencing factors are most closely associated with ground collapse and subsidence in Hangzhou, we collaborated with experts from the Hangzhou urban geological safety assessment at the Zhejiang Geological Survey.

Based on field inspections and expert analyses, ground collapses in the study area are primarily attributed to the following factors: geological conditions such as artificial fill, sandy loam, and concealed ditches; deficiencies in underground drainage pipe structures; hydrogeological influences; and disruptions caused by human engineering activities. Meanwhile, ground subsidence is mainly due to the study area being in a plain, with the distribution of soft soil layers, human activities, and hydrological factors being the primary reasons for ground subsidence occurrences. Given these factors, we identified 9 key factors as preliminary evaluation indicators and conducted a correlation analysis to prevent issues such as overfitting or frequent misjudgments in the machine learning process, as depicted in the correlation heatmap (Fig. 3 ). The evaluation factors used for the disaster, data sources, and data attributes are detailed in Table 1 and Fig. 4 .

Correlation heatmap of evaluation factors.

Assessment factors used in our research.

Random forest—back propagation neural network coupling model

To further enhance model accuracy and ensure that when predicting ground collapse disasters, the small scope of disaster areas leading to fewer data points does not impact the prediction results, we propose the Random Forest - Back Propagation Neural Network coupling model. Random Forest represents a collaborative approach in machine learning, comprising numerous decision trees working in unison 28 , 29 . Each tree receives a randomized subset of data and features, enhancing the model’s overall accuracy and versatility. This approach excels at managing a diverse array of inputs and discerning obscure patterns. The operation of Random Forest can be concisely expressed using the following equations to enhance the understanding of its ensemble methodology:

where \(Var(S)\) represents the variance of the target variable in the entire dataset \(S\) , \(|{S}_{left}|\) and \(|{S}_{right}|\) denote the number of samples in the left and right subsets post-split, respectively. Equation ( 1 ) highlights how Random Forest effectively reduces overfitting by incorporating diverse data samples.

where \({p}_{i}^{2}\) indicates the proportion of the samples in set \(S\) that belong to class \(i\) , and \(n\) is the total number of classes. This measure is critical in determining the best split at each node within the trees. The Eq. ( 2 ) not only allows Random Forest to handle a variety of input types effectively but also enhances its capability to detect subtle patterns in complex datasets.

Conversely, the Backpropagation Neural Network is a pivotal component in machine learning, particularly adept at complex tasks that defy linear analysis 30 , 31 . It comprises multiple layers and enhances its predictive capability through iterative adjustments of its strategy (weights and biases). To further elucidate the learning process within a Backpropagation Neural Network, the following equations can be considered:

where \({W}_{ij}^{\left(old\right)}\) and \({W}_{ij}^{\left(new\right)}\) are the old and new values of the weight between nodes \(i\) and \(j\) , \(\eta\) is the learning rate, and \(\frac{\partial \mathcal{L}}{\partial {W}_{ij}}\) represents the gradient of the loss function \(\mathcal{L}\) with respect to the weight \({W}_{ij}\) Eq. ( 3 ) delineates the core mechanism by which the network learns by iteratively adjusting its weights.

where \(\sigma \left(x\right)\) is the sigmoid activation function, which normalizes the input \(x\) into an output range between 0 and 1, enabling the network to handle non-linear relationships within the data. Equation ( 4 ) illustrates how the sigmoid activation function enables the neural network to transform linear inputs into outputs bounded between 0 and 1, facilitating the handling of probabilistic decisions and non-linear complexities.

To optimize our Random Forest Classifier, we conducted a grid search exploring various hyperparameters 32 , including the number of trees (ranging from 50 to 200 in increments of 50) and max features (options including 'auto', 'sqrt', and 'log2'). The optimal configuration was determined to be 100 trees, ensuring repeatability with a fixed random seed of 42. Similarly, for the Neural Network Classifier, our grid search covered different network architectures, focusing on varying the number of neurons in the hidden layers (options including 50, 100, and 150 for the first layer and 25, 50, and 75 for the second layer) and the maximum number of iterations (500, 1000, and 1500 iterations were tested). The most effective configuration found consists of two hidden layers with 100 and 50 neurons respectively, with a maximum of 1000 iterations, again using the random seed of 42 to maintain consistency. Each set of parameters was evaluated using 5-fold cross-validation 33 , ensuring that our selection process was robust and the results reliable. This comprehensive approach to hyperparameter tuning enhances the individual models' predictive accuracy before integrating them into the Stacking Classifier. The Stacking Classifier utilizes these two models as base models and integrates their predictions using another Random Forest configured with 100 trees as the final meta-model to make the ultimate decision. Subsequently, the Backpropagation Neural Network refines the analysis with its specialized capabilities. Together, they constitute a robust model adept at assimilating extensive information, distilling it, and producing precise predictions. The principle of the ensemble model is depicted in Fig. 5 .

Schematic diagram of RF-BP neural network coupling model structure.

Evaluation and analysis

Model performance analysis.

In this study, we selected 27898 data points using the "Raster to Point" function in ArcGIS, the sample size was determined by dividing the study area and evaluation factors into 32m x 32m pixels. Under these sample conditions, the dataset maintained relative balance, the computation time was reasonable, and subsequent model evaluation metrics also demonstrated the high accuracy of the model predictions. For ground subsidence susceptibility evaluation, susceptible areas were delineated using regional cumulative subsidence data. To ensure model training accuracy, during the ground subsidence susceptibility evaluation, 70% of the total data were randomly extracted for the training set using Python software. For ground collapse susceptibility evaluation, a 1:1 ratio of ground collapse disaster points to non-disaster points was employed to segment the training set (with disaster points labeled as 1 and non-disaster points as 0). Due to the limited scope of collapse areas, we obtained a total of 300 collapse data points, from which we randomly selected 210 collapse points and 210 non-collapse points to serve as the training set. This balanced approach helps to ensure that the model is not biased towards the more prevalent non-collapse conditions. The trained model was subsequently used to predict the remaining points, providing the probability of ground collapse for each pixel (ranging from 0 to 1) and the predicted cumulative subsidence value for each pixel.

To further demonstrate that our Random Forest-Back Propagation Neural Network Coupling Model outperforms individual models and ensures optimal results for susceptibility mapping, we evaluated the model's performance using multiple metrics. Since ground collapse prediction is a binary classification problem in our multi-hazard assessment, we primarily used metrics including ROC curves, AUC values, Accuracy, Precision, Recall, and F1-score.

The AUC (Area Under the ROC Curve) represents the model's overall performance across all classification thresholds, with a higher AUC indicating superior classification capability 34 . Accuracy measures the proportion of correctly predicted instances (true positives and true negatives) out of the total instances, reflecting the model's general effectiveness. Precision evaluates the proportion of true positive predictions among all predicted positives, indicating the model's reliability in predicting positive instances. Recall assesses the proportion of actual positive instances correctly identified by the model, demonstrating its ability to capture positive cases. The F1-score, which is the harmonic mean of precision and recall, provides a balanced measure of both metrics, especially useful for imbalanced datasets. Higher values for these metrics signify better model performance on the given dataset 35 .

Results showed that the stacked model outperformed others in all metrics in ground collapse, as illustrated in Fig. 6 a and b. Following the validation of the stacked model's performance, we employed it to predict susceptibility to non-binary tasks of ground subsidence. The results yielded high AUC values: 0.99 for less than 24mm (low susceptibility), 0.99 for 24mm-64mm (moderate susceptibility), 0.97 for 64mm-96mm (high susceptibility), and 0.99 for 96mm-128mm (very high susceptibility), indicating the model’s high predictive accuracy. The average AUC value of over 0.98 confirms the model's accuracy in predicting ground subsidence in our study and underscores its potential application for non-binary classification tasks. The specific ROC curves and AUC values can be seen in Fig. 6 c.

( a ) The ROC curves and AUC values in the ground collapse prediction task; ( b ) The Accuracy, Precision, Recall, and F1-score in the ground collapse prediction task; ( c ) The ROC curves and AUC values of the stacking model in the ground subsidence prediction task.

Susceptibility analysis

After the model’s prediction was completed, the RF-BP Neural Network Model’s results were used as a benchmark to import all grid points into ArcGIS 10.8 for evaluating the susceptibility zones of ground collapses and ground subsidence. First, regarding single-hazard susceptibility maps, for ground collapse, the probability of occurrence in the study area (ranging from 0 to 1) was reclassified using the equal interval method. This led to its division into four categories: low susceptibility (0–0.25), medium susceptibility (0.25–0.5), high susceptibility (0.5–0.75), and very high susceptibility (0.75–1). Specifically, Fig. 7 a shows the susceptibility map of ground collapses in the study area under this classification, and Table 2 details the specific susceptibility area, its percentage of the total area, and the distribution of disaster cases in the study area. For ground subsidence, the model’s predicted subsidence map was compared with the actual monitored cumulative subsidence map. Susceptibility areas based on cumulative subsidence were categorized as low (0–24 mm), medium (24 mm–64 mm), high (64 mm–96 mm), and very high (96 mm–128 mm) susceptibility areas. Subsequently, the overlap degree was calculated using the grid pixel data. Statistically, the overlap between the actual and the model-simulated cumulative subsidence was 90.31%, with specific overlap degrees for each interval detailed in Table 3 . This also reflects the accuracy of the stacking model. Figure 7 b shows the susceptibility map of ground subsidence in the study area.

( a ) Susceptibility map of ground collapses; ( b ) Susceptibility map of ground subsidence.

For the comprehensive susceptibility map of hazards, we employed two approaches. First, three experts from the Zhejiang Geological Survey were invited to reference the basic data of the two primary hazards affecting the study area, ground collapse and ground subsidence. They combined this information with their understanding of the study area, using the Analytic Hierarchy Process (AHP) to determine the impact magnitude (weights) of these two hazards on the study area. This process entails decomposing decision-making elements into hierarchies, including objectives, criteria, and alternatives, followed by qualitative and quantitative analysis to determine the weights of these disasters in the study area. The objective layer in the judgment process focused on the weight values of ground collapse and subsidence, while the criteria layer comprised ten indicators, including the impacts on the economy and human safety, relationship with geological conditions, current monitoring and management status, susceptibility assessment results, and causes and probabilities of occurrence. Of these, the first five indicators were weight determinants for ground collapse, and the latter five pertained to ground subsidence. Finally, by summing the weights of the disaster indicators for ground collapse and subsidence, the overall weight of the disaster was ascertained, leading to an aggregate judgment on the weights of multi-hazard indicators. The specific AHP judgment table and the results are shown in Table 4 and Fig. 8 .

( a ) The result of AHP assessment; ( b ) Comprehensive susceptibility map based on the AHP assessment. (This figure was created using ArcGIS Pro software. Desktop GIS Software|Mapping Analytics|ArcGIS Pro (esri.com)).

Second, we adopted a common overlay evaluation method used in multi-hazard susceptibility assessments 36 , 37 . This method involves overlaying susceptibility maps of individual hazards to determine the risk of different areas experiencing various hazards. For example, it helps to identify regions at high risk for a single hazard, areas at high risk for multiple hazards simultaneously, or areas where multiple hazards are unlikely to occur. Although this overlay method is relatively simple, it greatly reduces subjective judgments and, assuming the individual hazard susceptibility maps are accurate, provides highly valuable reference data. We selected areas with high and very high susceptibility levels from the four susceptibility categories. In Fig. 9 , the three colors represent areas in the study region with high risks of ground subsidence, ground collapse, and both disasters simultaneously. The remaining areas represent regions with low risk for both types of disasters.

Comprehensive susceptibility map using overlay evaluation method. (This figure was created using ArcGIS Pro software. Desktop GIS Software | Mapping Analytics | ArcGIS Pro (esri.com)) (Map image is the intellectual property of Esri and is used herein under license.

Prediction optimization

In the process of assessing regional disaster susceptibility using machine learning models, optimization is essential to achieve more accurate predictions. In our study, we focused on two main aspects of optimization: first, we employed grid search to obtain the optimal hyperparameters for individual models, ensuring the best performance of the stacked model; second, we optimized the dataset by using multi-source data and selecting an appropriate pixel size (32 m*32 m) to ensure that the dataset, particularly for the binary classification task of ground subsidence prediction, was not extremely imbalanced between disaster and non-disaster points.

Although we adopted reasonable methods to achieve good predictive accuracy, we acknowledge there is still room for improvement. For instance, we could explore different data partition ratios. In our case, we used a 70%:30% ratio for the training and test sets. While this ratio is widely used in many established cases of geological hazard susceptibility mapping, other ratios, such as 80%:20% 38 , might be more optimal for different scenarios. Also, Sameen 39 proposed a systematic subdivision method that captures training samples well-representative of the entire dataset. By subdividing the training/testing set based on Hellinger distance and applying a minimization method to reduce feature interdependence, they successfully enhanced the predictive capability of landslide susceptibility models.

Additionally, considering more multi-source data and evaluation metrics can improve the assessment results and increase the credibility of model predictions. In our predictions of ground subsidence and ground settlement susceptibility, we selected 7 and 6 evaluation metrics, respectively, based on field investigations and expert discussions. While these were reasonable choices, future work could include more metrics to enhance model robustness. Finally, for model hyperparameter optimization, we chose the commonly used grid search method due to the relatively simple nature of our dataset, leading to satisfactory optimization results. However, when considering more evaluation metrics and additional sample points, evaluating and quantifying model uncertainty 40 or opting for more efficient search methods, such as ant colony clustering algorithm in random search 41 or Bayesian optimization 42 , can yield better optimization results.

Prediction interpretability

The "black box" effect of machine learning models often leads to their predictive results not being directly trusted by urban decision-makers. Understanding the influence of data on model decisions and the model judgment process has become increasingly important among scholars. In our model, we used a Random Forest (RF) model, which acts as the final meta-model, to assess feature importance, specifically, feature importance is derived by calculating each feature's cumulative contribution to impurity reduction across multiple decision trees, then averaging and standardizing these contributions. As shown in Fig. 10 , in predicting ground subsidence, the thickness of the surface fill layer and rainfall (weekly) (2022) contribute significantly. In predicting ground settlement, aside from the density of the drainage pipe network and burial depth of the underground confined water level, other factors also have notable contributions.

Feature importance in predicting ground subsidence and collapse.

While our method provides the contribution of each evaluation factor to the model output, this explanation might not be comprehensive. Recently, SHAP (SHapley Additive exPlanations), which uses Shapley values from game theory to analyze and illustrate the impact of each input feature on model decisions, has become a popular choice among scholars 43 , 44 . However, its application in ensemble models, especially those combining different types of models, has not yet been reliably verified. This is an area that we may need to consider in future research. Additionally, integrating physical models with machine learning models to evaluate disaster mechanisms, rather than solely focusing on susceptibility assessment, often yields more convincing results 45 , 46 .

This study focused on a typical plain area in Hangzhou affected by urban geological hazards, creating susceptibility maps for the primary geological hazards in the study area: ground subsidence and ground collapse. The specific conclusions are as follows:

To obtain reliable and reasonable susceptibility assessment results, we conducted field investigations and discussions with the Zhejiang Geological Survey, and selected nine evaluation factors with low correlation coefficients, including seven for ground collapse and six for ground subsidence. Then we used a pixel size of 32 m × 32 m, with 27,898 data samples for model prediction. After optimizing the model using the grid search method, we obtained an optimized Random Forest—Back Propagation Neural Network Coupling Model. By introducing single models and comparing with SVM and logistic regression models, the results showed that the ensemble model improved the AUC, Accuracy, Precision, Recall, and F1-score by 3% to 40% in the binary classification task of ground collapse prediction. For the non-binary task of ground subsidence prediction, the average AUC value reached 0.98.

To achieve the highest accuracy in susceptibility mapping results for the study area, we ultimately selected the best-performing stacked model's prediction results to create susceptibility maps for ground collapse and ground subsidence. To further evaluate the overall hazard situation in the study area, we sought assistance from three experts from the Zhejiang Geological Survey. Using the AHP method, the study assessed the impact weights of ground collapse and ground subsidence on the study area and created a comprehensive hazard susceptibility map. Additionally, we used the traditional overlay method to objectively determine the hazard risk in different areas. After completing the mapping, we investigated the feature importance during the prediction process. The results indicated that for ground collapse prediction, the thickness of the surface fill layer and weekly rainfall (2022) were the most significant contributors. For ground subsidence prediction, besides the density of the drainage pipe network and burial depth of the underground confined water level, other factors showed significant contributions.

Data availability

All data generated or analyzed during this study are included in this published article.

Code availability

Name of the code/library: RF-BP Neural Network Coupling Model Contact:[email protected]. Hardware requirements: Processor: A multi-core processor is recommended for efficient running of machine learning models. Memory: At least 8 GB RAM is advised for effective processing of the datasets and machine learning models. Storage Space: Sufficient storage space to accommodate the datasets, model files, and output files. Program language: Python. Software required: Python Interpreter, preferably version 3.8 or higher. Python Libraries: pandas, scikit-learn, joblib, matplotlib. Excel or a compatible software for reading and writing Excel files. Program size: code:4 KB data:818 KB model:5463 KB. The source codes are available for downloading at the link: https://github.com/xygbb/RF-BP-Neural-Network-Coupling - Model2.git.

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Acknowledgements

This research is supported by the China Geological Survey, Nanjing Center, Zhejiang Geological Survey and China University of Geosciences, Wuhan. The work described in this paper was funded by Laboratory of Geological Safety of Underground Space in Coastal Cities, Ministry of Natural Resources (Project No. BHKF2022Z02), and the China Geological Survey, Nanjing Center (Project No.DD20190281).

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Yu, B., Xing, H. & Yan, J. Susceptibility assessment of multi-hazards using random forest—back propagation neural network coupling model: a Hangzhou city case study. Sci Rep 14 , 21783 (2024). https://doi.org/10.1038/s41598-024-71053-7

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Reaching China’s fertilizer reduction goals through nitrogen and phosphorus recovery: a substance flow analysis case study

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• Julia Santolin   ORCID: orcid.org/0000-0003-2642-8307 1 , 2 ,
• Oliver Christopher Larsen   ORCID: orcid.org/0000-0002-4361-100X 1 ,
• Albrecht Fritze   ORCID: orcid.org/0000-0002-2818-3246 1 ,
• Bing Xue   ORCID: orcid.org/0000-0002-7790-1216 1 ,
• Zheng Yang   ORCID: orcid.org/0000-0002-2176-6297 1 &
• Vera Susanne Rotter   ORCID: orcid.org/0000-0001-9300-7292 1  

Linear agricultural nutrient regimes are the principal cause for perturbation of the geochemical cycles for nitrogen (N) and phosphorus (P) and other planetary boundaries. Nutrient cycles are characterized by high spatial disparity and China is a hotspot due to high fertilizer application rates. Using substance flow analysis, this study identified and quantified nutrient flows from agricultural production to residue management of Huangyan tangerines ( Citrus reticulata ) and water bamboo ( Zizania latifolia ) in a case study of Huangyan district (Taizhou City, Zhejiang province). About 754 Mg/a of N and 105 Mg/a of P can theoretically be recovered in the tangerines and water bamboo systems from currently untapped material flows. This could replace 59% of the N and 15% of the P currently applied as chemical fertilizer, reducing environmental impacts. Combining the nutrient recovery of both systems and upscaling the results to Taizhou City, the goal from the 14th Five-Year Plan for Agricultural and Rural Modernization to save 1182 Mg of nutrients per year could be exceeded by almost 12 times. This study’s data have varying degrees of uncertainty. The analysis of data representativeness shows potential for improvements, especially in the agricultural production of water bamboo and the nutrient contents of material flows.

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Introduction

The biogeochemical cycles have exceeded the proposed safe operating space for humans [ 1 ]. According to Campbell et al., agriculture is the main driver for the transgression of this and other planetary boundaries [ 2 ]. Specifically, the production of nitrogen (N) fertilizer is linked to a high energy demand (the Haber–Bosch process for ammonia synthesis is responsible for 1–2% of the world’s total energy consumption) [ 3 ], it consumes 2% of the world’s natural gas as feedstock [ 4 ], and contributes to 1.4% of all anthropogenic CO 2 emissions [ 5 ]. Phosphorus (P) is a finite resource mainly mined in China, Morocco and the United States, making phosphate rock as well as phosphorus critical raw materials [ 6 ]. Apart from climate change and resource depletion, the high N and P application in agricultural regions leads to air pollution, soil acidification, and eutrophication of water bodies—which ultimately results in water dead zones, fish kills, algal blooms, and water contamination [ 7 ]. This unsustainable nutrient management attempts against the achievement the United Nations Sustainable Development Goals (e.g. 6—Clean water and sanitation, 12—Responsible consumption and production, 14—Life below water, 15—Life on land).

Industrial agricultural systems are commonly characterized by linear regimes. Since the nineteenth century, natural nutrient sources and recycled materials were no longer enough to cover the needs of the increasing population [ 7 ]. Therefore, the use of Haber–Bosch N and mined P started to increase rapidly, becoming the main nutrient input for crops—since the 1960s, the use of synthetic N fertilizers increased ninefold and the P fertilizer use tripled [ 7 ]. Although fertilizer production is concentrated in a few countries (mainly China with 25%, Russia with 10%, and United States and India both with 9%), its use is widely distributed globally, meaning that many countries rely on imports to cover their fertilizer demand [ 8 , 9 ]. After application, an important part of these nutrients (over 80% of the N and 25–75% of the P) gets lost to the environment, causing pollution [ 7 ]. The inefficient fertilizer use has been recognized as a global issue and the UN Environment Programme highlighted the need for coordinated policies to manage N and P pollution effectively at global, national, and regional levels [ 10 ]. Moreover, fertilizers are one of the carbon-intensive products covered by the EU’s Carbon Border Adjustment Mechanism (CBAM) to encourage global reduction of carbon emissions instead of moving their production to countries with less stringent climate policies [ 11 ].

China (in particular eastern China) is one of the few agricultural regions with very high P and N application rates that are the main contributors to the transgression of the biogeochemical flows boundary [ 1 ]. It is the world’s largest consumer of fertilizers (42.31 Mio Mg/a of nutrients) [ 12 ], and the country with the second highest greenhouse gas (GHG) emissions from agriculture after India (663 Mio. Mg of CO2 eq/a) [ 13 ]. The reason is that China’s agriculture has been transitioning from a self-subsistence extensive agriculture to an intensive industrial cash crop production system [ 14 ]. After the establishment of the People’s Republic of China in 1949, hundreds of millions of farmers were organized in collective agriculture communes, where all agriculture production decisions were made by local leaders following a higher level production plan [ 15 ]. This changed after the economic reform in 1978: collectively owned land was leased to individual farmers, who had to deliver a fixed quota of “strategic crops” to the state for a fixed price, but were also free to produce more and sell their surpluses in rural markets [ 15 ]. To increase the production on their small plots, farmers started to apply excessive amounts of chemical fertilizer—China’s yearly application per hectare of cropland is one of the highest of the world with 319 kg (for comparison, the world’s average is 119 kg and Europe’s average, 75 kg) [ 16 ]. This resulted in a series of environmental impacts, including groundwater contamination with nitrates, eutrophication of surface waters, soil acidification, greenhouse gas emissions, loss of biodiversity, and micronutrients deficiencies in feed and food [ 17 ].

The Chinese government has set goals and introduced policies to improve sustainability in agriculture. In 2015, the Ministry of Agriculture launched the “zero-growth” action plan, regulating fertilizer and pesticide use by 2020 [ 18 ]. Later, in 2021, the 14th Five-Year Plan for Agricultural Green Development was released, emphasizing the reduction of chemical fertilizer and pesticide use and the improvement of the utilization level of agricultural resources [ 19 ]. China wants to become carbon neutral by 2060, which requires a substantial transformation of the agricultural sector as well [ 20 ].

In addition, local governments are increasingly taking measures to promote agricultural practices that are more circular and sustainable. In Taizhou, a city in the Zhejiang province, the Bureau of Agriculture and Rural Affairs launched its own 14th Five-Year Plan for Agricultural and Rural Modernization to improve productivity and living standards in rural areas (its focus is slightly different of that of the national Plan for Agricultural Green Development mentioned above, which mainly aims at reducing environmental impacts). This action plan aims to increase the use of commercial organic fertilizer, digestate from anaerobic digestion, and green manure to improve soil structure and organic matter content. The utilization rate of manure (from livestock and poultry) and rice straw should also be improved to 92% and 95%, respectively, by 2025. Besides, chemical fertilizer use in the crop sector should be reduced with the help of soil testing and formula fertilization. In this way, Taizhou expects to save 0.6 kg of “pure nutrients” (N, P 2 O 5, and K 2 O) per Mu—or more than 1182 Mg per year—while reducing air pollution (mainly caused by straw burning), eutrophication of water bodies, soil erosion, and salinization. [ 21 ]

Implementing circular systems to achieve these goals requires the detailed study of locally available, potentially valuable organic material flows, which can be done by using Material Flow Analysis (MFA) [ 22 ]. This is a case study for Huangyan (黄岩), a district in Taizhou city (Fig.  1 ) [ 23 ]. Huangyan is a typical example of a region with a linear, cash-crop-oriented, agricultural system and a high demand for chemical fertilizers. While the majority of Taizhou’s economic activities take place in Luqiao district, the agricultural production is based in Huangyan. The agricultural sector, with a yearly contribution of over 10 billion yuan, plays an important role in the region’s economy [ 24 ]. In 2021, 1,918,000 Mu of agricultural land were sown in Taizhou, with a total output of 560,000 Mg of grain and 1,456,900 Mg of fruit [ 25 ]. By quantifying the nutrients that could be recovered in this region, the possible contribution to Taizhou’s goal can be assessed and additional measures can be taken (e.g. to effectively recover those nutrients, to formulate stricter goals if necessary, or to introduce new regulations).

Map of Huangyan, a district in Taizhou city, located in the Jiaojiang River Delta, southeast of Zhejiang Province. Huangyan has an area of 988 km 2 and a registered population of around 610,000

The study focuses on the two crops with the highest production amounts in the region, namely Huangyan tangerines ( Citrus reticulata, annual production in Taizhou reaches 546,000 Mg/a) and water bamboo ( Zizania latifolia, also called Manchurian wild rice, 77,000 Mg/a) [ 25 ]. Both species are native to China, which leads the global market—China produces 61% of the world’s tangerines, mandarins, and clementines, and 27% of the rice [ 26 , 27 ]. The goal of the study is to identify and quantify all the by-product flows in these agri-food systems, to later derive the amounts of N and P that could theoretically be recovered and recycled. These theoretical recycling potentials will then be related to the amount of nutrients that Taizhou expects to save according to its last Five-Year Plan for Agricultural and Rural Modernization. In this way, the potential contribution of nutrient recovery in these two agri-food systems can be measured.

Materials and methods

The methodology of material flow analysis, deeply described in Brunner & Rechberger’s Handbook of Material Flow Analysis , is defined as “a systematic assessment of the flows and stocks of materials within a system defined in space and time” [ 22 ]. MFA is an iterative method consisting of several steps, including goal and system definition (which lead to a qualitative model), determination of mass flows and stocks, and mass balance (resulting in a quantitative model). The quantified material flows can also be linked with the substances’ mass fractions to identify the substance-specific sources and sinks, allowing the development of specific recommendations to improve substance flows.

Goal and system definition

The goal of this substance flow analysis (SFA) is to quantify the amount of N and P that could be recovered within the agri-food systems of the two main agricultural products (Huangyan tangerines and water bamboo) in Huangyan district, Taizhou City, Zhejiang province, China, in 2019.

The system model was defined according to the material life cycle stages identified during the data acquisition, namely: agricultural production, manufacturing, distribution and sales, consumption, and waste treatment and disposal (Figs.  2 , 3 ). The processes shown in the SFAs represent the average and not the best available technology. All solid organic material flows were considered. Gaseous, water, and energy flows were not regarded due to a lack of data.

System definition for Huangyan tangerines

System definition for water bamboo

Data acquisition and uncertainties

The required data were acquired by both top-down (secondary data comprising statistical and aggregated data) and bottom-up (primary data from interviews) data collection.

For the bottom-up data collection, 25 relevant stakeholders from governmental institutions, educational organizations, agricultural and manufacturing sectors, markets, and waste management companies were interviewed between October and November 2019 (supplementary material, Figure a). The interview participants were selected through snowball sampling. Interview guides were prepared in advance to provide a framework of topics to be covered (see questions in supplementary material). However, the interviews were semi-structured, including open questions and allowing new ideas to be raised during the discussion. A translator was always present to translate from Chinese to English and vice versa.

Top-down data were collected through literature research, including statistical yearbooks (from Huangyan and Taizhou), scientific publications, and official reports. This secondary data were combined with the primary data from the interviews to have a solid foundation for the MFA modelling.

For the SFA, the material composition data was taken from FoodData Central, a data system launched by the U.S. Department of Agriculture (USDA), whenever available [ 28 ]. If the needed data were not available in that system, different sources were revised, and the average of various values was calculated.

To account for uncertainties and varying reliability, as well as the temporal and spatial representativeness of the collected data, four data representativeness levels [ 29 ] were defined to classify the quality of the gathered data (Table  1 ). Level 1 was assigned to educational organizations (interviewees were experts in their fields); level 2 to governmental institutions and waste treatment companies (statistical data derived from reports, measurements, and census in the study region); level 3 to farmers, food manufacturing companies and markets (specific information, not valid for the entire region); and level 4 to literature data (related to other geographic regions and/or periods).

Modelling and material balancing

Mass flows of fresh matter (FM) were determined using an Excel model. All the inputs and outputs of each process were related to a reference flow of 1 Mg of freshly harvested product (Huangyan tangerines or water bamboo). When a range of values was available, an average was used. The calculations to determine each of the FM flows and the assumptions made can be found in the supplementary material (Tables a, b).

The flows for the N and P SFAs were calculated by multiplying the FM flows by the N and P mass fractions of each flow. These mass fractions were obtained from secondary sources, except for a few cases, where the interviews revealed relevant data (supplementary material, Tables c, d).

The models for Huangyan tangerines and water bamboo were introduced in the MFA software e!Sankey to obtain a graphical visualization of the nutrient flows. Finally, the theoretical recycling potential of P and N was calculated by adding up all the by-product flows and compared to the amount of N and P already being recycled.

These results were compared with the goal set by Taizhou’s Five-Year Plan for Agricultural and Rural Modernization (saving 1,182 Mg/a of “pure nutrients”). To do that, the values for the P recycling potential were multiplied by 2.29 to account for P 2 O 5 and, hence, allow the comparison with the above-mentioned goal.

The results for Huangyan tangerines and water bamboo are described in this section (the graphic descriptions of the entire life cycles of the tangerines and the water bamboo can be found in Figs.  2 , 3 ). The SFAs for N are illustrated in Fig.  4 (tangerines) and Fig.  5 (water bamboo), and those for P are shown on Fig.  6 (tangerines) and Fig.  7 (water bamboo).

Nitrogen SFA for Huangyan tangerines. Values represent annual flows

Nitrogen SFA for water bamboo. Values represent annual flows

Phosphorus SFA for Huangyan tangerines. Values represent annual flows

Phosphorus SFA for water bamboo. Values represent annual flows

Huangyan tangerines

Agricultural production.

Around 4,200 ha in Huangyan are covered by tangerine orchards. This area is shared between almost 19,500 farms, i.e. the average area of a tangerine farm in Huangyan is only 0.2 ha [ 24 ]. Most of this area belongs to families who own a small piece of land for self-supply. Recently, the government is investing to improve the quality of Huangyan tangerines by funding large, modern tangerine gardens managed by just a few partners [ 30 ]. An average tree produces around 24 kg of tangerines per year [ 31 ]. Trees in their most productive phase, however, can produce up to 10 times more [ 32 ]. The young tangerine gardens in the district are the main reason for the low average [ 30 ].

Tangerine farmers apply 20–30% (relative to N) organic fertilizer and 70–80% chemical fertilizer (15% N, 15% P 2 O 5 , 15% K 2 O) [ 31 ]. In 2017, Taizhou launched a policy to promote the use of organic fertilizer: farmers who use at least 50% organic fertilizer can get access to subsidies [ 31 ]. Currently, there are less than 50 of these “green agriculture” farms in Huangyan—including but not only tangerine farms [ 32 ]. Since there is no fertilizer production in Huangyan, this product has to be imported from other regions [ 31 ]. Chemical fertilizers add 975 Mg of N and 426 Mg of P to the agricultural soils every year, constituting the largest nutrient input of this system. Common organic fertilizers include rapeseed compost, a mixture of sheep manure and mushrooms, compost made out of cassava and residues from alcohol production, and compost made out of water bamboo and sugar cane waste [ 31 , 32 ]. These organic fertilizers introduce 325 Mg of N and 195 Mg of P to the tangerine system.

Most of the tangerines produced in Huangyan (95%) are exported to other regions [ 24 ]. 173 Mg of N and 11 Mg of P leave the system in this way. From the rest, 95% is sold as fresh fruit directly on the farm or in markets and supermarkets (or grocery stores), and 5% serves for the further manufacturing of different products like canned tangerines, Chinese medicine, oil, or candies [ 33 ]. The largest by-product flow in the entire tangerine system comes from the agricultural stage. Every year, 16,140 Mg of by-products are produced in Huangyan’s tangerine farms. This agricultural waste, consisting mostly of pruning residues, contains 311 Mg of N and 20 Mg of P. It is partly used to make fire for heating and cooking [ 33 ], while the rest is either left on the ground, burned in open fires, or landfilled [ 30 , 31 ]. Farmers mentioned a lack of space (it is not permitted to construct buildings in agricultural areas) and a lack of animal manure as the main reasons why they do not compost or digest their waste [ 32 ].

Manufacturing

The biggest company for canned fruit in Taizhou City, “Yiguan Food”, contributes to 10% of China’s canned tangerines production [ 31 , 32 , 33 , 34 ]. The majority of their products are exported and only small amounts (5%) stay in Taizhou for supermarkets, cake and jelly production [ 35 ]. The tangerines for the manufacturing process are purchased from different cooperatives in Taizhou, Hubei, Hunan, and, mostly, Linhai [ 36 ]. The production process includes size separation (small tangerines are picked out), heating in water to facilitate the peel separation, and an acid–base treatment to separate the pith. Afterward, tangerines are separated into slices by hand, which in some cases damages them. Peels, damaged or rotten tangerines, pith, and wastewater are the major by-product flows in this production chain. The peels are sold to a company that produces spices. Wastewater is sent to an industrial treatment plant that processes wastewater from this and other companies, before going to the municipal wastewater treatment plant.

Distribution

Huangyan’s tangerines for fresh consumption are either sold directly from the farm (30%) or in markets and supermarkets (70%) [ 37 ]. Only 9% of the products in the market come from Huangyan, while the rest is imported from other regions, for example from the wholesale market in Luqiao [ 38 ]. Imported tangerines introduce 60 Mg of N and 4 Mg of P into the system. Around 5% of the products sold in the market get wasted [ 39 ]. A small part of these by-products is collected by people who use it to feed their animals, but most of it goes to Huangyan’s landfill [ 40 ]. In contrast, the wholesale market in Luqiao treats part of its by-products: the “clean” fraction (without plastic, paper, or other contaminants) is treated at high temperatures to produce fertilizer. The “contaminated” fraction is compressed. The wastewater then goes to the wastewater treatment plant and the compressed waste is incinerated at Luqiao waste to energy plant. [ 39 ]

Consumption

Around 6% of the produced tangerines, containing 50 Mg of N and 2 Mg of P, get wasted in households [ 41 ]. The consumed nutrients are excreted and leave the households with the wastewater (16 Mg of N and 2 Mg of P).

Waste treatment

Huangyan Waste Sorting and Treatment Centre is responsible for 20% (or 27 Mg per day) of municipal perishable waste. Well-sorted perishable waste from school and office canteens, as well as the “clean” fraction of the perishable household waste is composted. This accounts for 20% of the perishable waste treated by the company. The composting process is still being tested, and the compost quality is still not good enough for agricultural applications. The rest 80% of the company’s perishable waste, corresponding to the “polluted” fraction of the household waste, is treated anaerobically. This waste is first filtered, and then the oil is separated and sold to soap or biodiesel companies. The solid fraction is treated for three to seven days under anaerobic conditions and high temperatures (around 140 °C), while the liquid fraction goes to the wastewater treatment plant. Also this treatment is still being tested to improve the quality of the resulting fertilizer. [ 42 ]

Most of Huangyan’s municipal perishable waste (80%) ends up in the landfill [ 42 ]. 40 Mg of N and 2 Mg of P get lost in this way. At the time of the field trip, the landfill was almost full, and a new incineration plant was being constructed to replace it. During the interview at the landfill, it was stated that China would ban landfills in 2020. There was a project to use kitchen waste to produce biogas in the future, but there was still no estimated starting date. [ 43 ]

Wastewater treatment

Excreta is the main waste flow resulting from the tangerine consumption stage, and the second-largest waste stream in the entire system (12,009 Mg/a). Yuanqiao wastewater treatment plant in Huangyan District can treat up to 60,000 m. 3 per day. The site covers an area of more than 11 ha and applies Anaerobic/Anoxic/Oxic technology (AAO). The clean effluent is discharged into the river. [ 44 ]

Water bamboo

Manchurian wild rice ( Zizania latifolia ), or water bamboo, is a perennial plant native to China [ 45 ]. Its seeds have been consumed as a cereal for more than 3,000 years. When infected with the black smut fungus ( Ustilago esculenta ), the stem becomes bigger and tender, making it the second most-cultivated aquatic vegetable in China. Huangyan is one of the main producing areas in the country [ 46 ]. Wetland farms growing Z. latifolia in Huangyan cover a much smaller area than tangerine farms—around 800 ha [ 37 ]. However, this area is growing because producing this crop in paddy fields is more profitable than producing rice [ 30 ].

There are two harvest seasons for water bamboo: one from May to June and another one from October to December [ 47 ]. In the summer, the production (around 100 kg/ha) is twice as much as in autumn [ 48 ]. To produce 1 Mg of water bamboo, farmers use on average 50 kg of chemical fertilizer (15–15-15) [ 24 ]. In this way, 296 Mg of N and 129 Mg of P are added to the cropland every year. Apart from that, in the summer, farmers put compost from their farms back in the field (503 Mg of N and 19 Mg of P per year) [ 48 ].

During the harvesting, waste leaves (which represent 30% of the plant’s weight) are cut off and, in most cases, left on the field [ 47 ]. This is the heaviest by-product flow in the entire system, accounting for 25,200 Mg per year (437 Mg of N and 147 Mg of P). There are some farms using these leaves to cover the soil (e.g. in tangerine fields) to improve its quality, although the transport and labour is expensive [ 49 ]. Stems are collected for further processing [ 47 ]. In the next step, the stems are peeled by hand. Thus, the water bamboo shoots (representing 50% of the plant’s weight) are separated from the peels (accounting for the rest 20%) [ 47 ].

Around 20 kg/ha of water bamboo shoots are wasted every year because of diseases, bad quality, or bad appearance. This agricultural waste stream, containing 64 Mg of N and 14 Mg of P, gets landfilled [ 24 ]. After the peeling process, the majority of the water bamboo shoots are exported, along with 648 Mg of N and 137 Mg of P. This is the largest P export in the system.

Farm composting

The peels are cut into little pieces on site and mixed with urea—the largest nitrogen flow in the system, adding 3,091 Mg of N—and decomposing agent. After 20 days, the compost is ready to be put back on the field. This is done every year at the end of July. 70% of the compost (1173 Mg of N and 44 Mg of P) is sent to other fruit and vegetable farms, constituting the largest N export in the system. The rest 30%, containing 503 Mg of N and 19 Mg of P, is used in the farm itself. [ 48 ]

Most of the produced water bamboo shoots (95%) are exported to other regions. The part that stays in Huangyan gets sold in markets, supermarkets, and grocery stores [ 24 ]. As mentioned for the tangerine system, only 9% of the products in the markets come from Huangyan, and about 5% of the products sold in the market get wasted.

Consumption, waste treatment, wastewater treatment

The life stages consumption, waste treatment, and wastewater treatment are identical to the ones described for the tangerine system. Also in, this case, excreta constitutes the major waste flow coming from the consumption stage (16,032 Mg/a). 286 Mg of N and 61 Mg of P are lost through this route.

Recovery potentials

In the tangerine system, the by-product streams that could theoretically be recycled include agricultural waste; peels, damaged tangerines, and pith from the manufacturing process; and excreta, peels, and rotten tangerines from the consumption process. These flows amount to 38,870 Mg/a. The nitrogen content in those flows adds up to 382 Mg/a and the phosphorus content to 25 Mg/a.

Only the tangerine peels from the manufacturing process are currently being recycled to produce spices and a part of the rotten tangerines and peels from consumption are treated anaerobically or through composting. These account for 2,115 Mg/a or 5% of the total theoretical recycling potential. The nitrogen contained in the recycled flows accounts for only 11 Mg/a or 3%, and the phosphorus for 0 Mg/a or 2% (Fig.  8 ).

Tapped and untapped recycling potential for nitrogen and phosphorus in Huangyan’s tangerine and water bamboo systems. Solid color areas represent the amount of N (green) and P (orange) that is already being recycled. Dotted areas represent the amount of N (green) and P (orange) that is not yet recycled. t tangerine system, wb water bamboo system

Regarding the water bamboo system, the theoretically recyclable by-product streams include leaves cut and put back into the field while harvesting; peels and rotten water bamboo from the peeling process; rotten water bamboo from the markets; and excreta and rotten water bamboo from consumption. Together, these flows amount to 63,685 Mg/a. The nitrogen content in those flows adds up to 1,122 Mg/a and the phosphorus content to 292 Mg/a.

The materials that are already recycled include water bamboo leaves and peels in the field and rotten water bamboo shoots that are sent to composting or anaerobic treatment after consumption. These flows add up to 42,166 Mg/a, or 66%, of the theoretical recycling potential for fresh matter. The nitrogen contained in the recycled flows accounts for 738 Mg/a or 66%, and the phosphorus for 211 Mg/a or 72% (Fig.  8 ).

Contribution to Taizhou’s goal

Adding up the recycling potentials of the untapped N and P 2 O 5 flows results in 426 Mg/a for Huangyan tangerines and 570 Mg/a for water bamboo (Fig.  9 ). The goal of Taizhou’s Bureau of Agriculture and Rural Affairs is to save 1,182 Mg of “pure nutrients” (N, P 2 O 5 , K 2 O) per year. Hence, recovering all the N and P from the analysed systems would contribute 36% to the achievement of the goal in the case of the tangerines and 48% in the case of the water bamboo. Combining both systems would make a very high contribution to the goal (84%).

Contribution of the potentially recyclable N and P 2 O 5 in both Huangyan systems (Huangyan tangerines and water bamboo) to the goal set by Taizhou’s Five-Year Plan for Agricultural and Rural Modernization on the mass of “pure nutrients” (N, P 2 O 5 , K 2 O) to be saved

Data uncertainties of material flows

The basis for the N and P SFAs for tangerines and water bamboo presented in Sect. “Results” are MFAs conducted in the scope of this study. Data uncertainties for the corresponding material flows are discussed hereunder. The below-mentioned reference flows correspond to 1 Mg of fresh matter (tangerines or water bamboo).

Data uncertainties in the tangerine system

The data representativeness of all flows entering or leaving the agricultural production process in the tangerine’s SFA corresponds to the first or the second level. The “organic fertilizer” input and the “pruning residues and leaves” output account for 21% of the reference flow. The size of these flows combined with their very high data reliability form a good basis for the SFA. The flow “tangerines for export” is the largest of the system, accounting for 90% of the reference flow, and it is defined with high reliability. Due to the flows’ significance, it is recommended to further improve data representativeness and confirm flow quantities by published scientific data or an independent source such as producers or distributors. Most input and output data of the canned tangerines production process was provided by one factory owner ( Yiguan Food ) and therefore was classified as medium reliability data. It could be argued that in reality data representativeness is higher, since it is the largest company producing canned tangerines in Taizhou City [ 31 , 32 , 33 , 34 ]. Further research could be conducted by examining other similar factories or conducting own measurements. The largest flow related to this process, however, only accounts for 7% of the reference flow. Hence, efforts to improve the data quality of this process should be kept within reasonable limits. Three of the four flows of the distribution process correspond to the third data representativeness level. Due to the significance of the “imported tangerines” (31% of the reference flow) and the “tangerines for the markets” (33%) flows, it is suggested to verify the gathered information. More interviews with owners of various markets in Huangyan should be conducted. It was assumed that the consumers are “steady state” humans, i.e. the nutrients consumed in the food will end up in the excreta, based on the fact that the percentage of food retained by the human body for the synthesis of tissues can be considered negligible on average [ 50 ]. Since this data comes from literature, those flows were classified as level four. The “Excreta to wastewater” flow is the largest output (1% of the reference flow) of the consumption process. Its data with defined medium data reliability was obtained from scientific publications of other geographic regions and periods. Since this flow holds a significant nutrient recovery potential, it is recommended to reduce data uncertainty and contact Taizhou’s Environmental Protection Bureau. Unfortunately, during this study, the Bureau repeatedly refused to be interviewed. Requesting a reference letter from the Chinese government could help to obtain data from governmental institutions. All the flows entering and leaving the composting, filtration, and anaerobic treatment processes belong to the data representativeness level 2, which indicates that these flows can picture the real situation in Huangyan relatively well.

Data uncertainties in the water bamboo system

The outputs of the agricultural production, “stems” and “leaves” account for 140% and 60% of the reference flow, respectively. Both flows are based on data from one farmer and are, therefore, defined as the third data representativeness level. Roughly 29% of the stems become peels. Together with the amount of rotten water bamboo shoots, it makes ca. 53%, which corresponds with the information obtained from Huangyan Agricultural Bureau—according to which 50% of the vegetable is wasted [ 30 ]. The “leaves” and the “peels” flows are the largest by-product flows in the system and represent the highest nutrient recovery potential. Based on the statements of two farmers (third representativeness level) the leaves are left in the fields during the harvest and the peels are composted. It is recommended to approach water bamboo experts (equivalent to the scientists from the Institute of Citriculture for the tangerines), identify relevant scientific studies, or conduct surveys covering a representative number of farms, to reduce data uncertainty for these relevant material flows. The data employed to model the rest of the processes (distribution, consumption, composting, filtration, and anaerobic treatment) is the same as the one used for the tangerines. Hence, the data representativeness of those processes in both systems is similar and the same recommendations can be drawn (see “ Data uncertainties in the tangerine system ”).

Data uncertainties in both systems

The fresh matter flows served as a basis for the calculation of the N and P flows. During the SFA modelling, the uncertain material flow values were multiplied by estimates for N and P contents obtained from secondary sources. Firstly, the level of uncertainty rises with these mathematical operations. Secondly, the values from the literature refer to studies with different spatial scopes decreasing the accuracy of the calculated P and N flows in this study. To improve accuracy and reduce uncertainty, it is recommended to conduct a sampling campaign to measure the N and P contents of each flow as a basis for the SFAs, as was done in a Danish study [ 51 ]. Although this approach would have exceeded the scope of this study, it could have avoided the need for several assumptions (supplementary material, Tables c, d).

Methodological uncertainties of the material and nutrients SFAs

The inputs and outputs of the substance flow processes are not always balanced (see Δ MB flows in the SFAs), since data on energy, soil, water, and gas flows could not be gathered in the scope of this study. The following two paragraphs discuss nutrient imbalances. The mentioned values represent the real annual flows in Huangyan.

Methodological uncertainties in the tangerine system

The biggest N losses occur as agricultural waste during the tangerine production (311 ± 31 Mg/a) and as peels during the consumption phase (50 ± 10 Mg/a). The N mass fraction of the peels is higher than that of the rest of the fruit. Since most of the peels produced during the consumption phase (80%) are sent to the landfill, this organic material is lost from the system. 807 ± 161 Mg N/a are missing when comparing N from fertilizer application (inputs) and N contents in agricultural products and by-products (outputs). From the applied 1,300 ± 130 Mg N/a, only 13% (173 ± 35 Mg/a) end up in the tangerines. The findings align with previous research, which shows that agriculture is responsible for almost three quarters of all N losses (43% of those losses occur through nitrate leaching to ground and surface waters, 30% through denitrification, and 23% through ammonia emissions) [ 52 ]. Similarly, major P losses in the tangerine system occur during agricultural production. While 621 ± 62 Mg P/a are applied to the tangerine fields, 20 ± 2 Mg/a end up in agricultural waste and 12 ± 2 Mg/a (2%) in produced tangerines. The rest 589 ± 118 Mg P/a (95%) is lost. Prior research has also showed that more than half of the total P losses happen in agriculture, 88% of those losses through P accumulation in soils [ 52 ]. According to George [ 53 ], agricultural production has low P-efficiencies due to solubility and mobility interactions in soils and plants. Also, Golomb and Goldschmidt [ 54 ] stated that less than half (43.7%) of the P-uptake by the mandarin trees ends up in the fruits. The pruning residues and leaves to product ratio calculated in a Croatian study is much lower than the one resulting from this study (0.07 kg/kg versus 0.21 kg/kg) [ 55 ]. This can be explained by the new tangerine farms in Huangyan, since young trees have lower production rates leading to relatively higher amounts of residues [ 30 ]. The pruning residues and leaves to product ratios are expected to decrease in the future, with more mature trees. These are also possible reasons for the low N-uptake of tangerines in Huangyan. Furthermore, the export of tangerines implies N and P losses for Huangyan’s tangerine system, with 176 ± 36 Mg N/a (14%) and 12 ± 2 Mg P/a (2%). No information was found on the local wastewater treatment processes. The literature research indicated that wastewater treatment plants in China are still concerned about removal—and not recovery—of nutrients, and that landfilling is the main sludge treatment method [ 56 ]. Hence, the nutrients contained in excreta (16 ± 6 Mg N/a, 2.4 ± 1.0 Mg P/a) are not recovered. A study conducted in Vietnam quantified regional N and P flows from rice, fruit, and vegetable production. Major P losses modelled in that study also occur during the same life cycle stages and include leachate from agricultural production, solid waste, and excreta from households [ 57 ]. Analyses of soil, surface water, groundwater, and wastewater samples, as well as liquid and gaseous emissions, could provide details on the fate of N and P in the agricultural production and consumption phase.

Methodological uncertainties in the water bamboo system

The production of water bamboo is characterized by higher N and P recovery rates than that of tangerines. Assuming that all nutrients from the leaves, which are cut off during the harvest process, are absorbed by the crops in the wetland, a total of 29% N (550 ± 165 Mg/a) and 56% P (166 ± 50 Mg/a) of the applied nutrients would be recovered. The differences between added nutrients from fertilizer and leaves (inputs) compared to harvested stems (outputs) are 425 ± 127 Mg N/a (22% of applied N) and 73 ± 22 Mg P/a (20%). Other studies investigating flooded rice production systems, showed that the largest losses for P and N were caused by run-off, leaching and accumulation in the soil, as well as emissions to air [ 58 , 59 ]. These potential nutrient losses should be quantified in future studies for the water bamboo production system with leaves decomposing in anaerobic conditions in flooded paddies and peels further processed to compost (19 Mg P/a).

The nutrient losses during the peeling, distribution and consumption phase are 384 Mg N/a and 81 Mg P/a from rotten water bamboo and excreta, which end up in the landfill or the wastewater treatment plant. 50% of the N (1,821 ± 481 Mg/a) and 95% of the P (181 ± 41 Mg/a) entering the system as fertilizers are exported as water bamboo and composted leaves.

In summary, for the agricultural processes, nutrient fixation in soil and nutrient leaching in surface and ground water, as well as gaseous emissions, are assumed to be relevant contributions to the substance imbalances. For the remaining processes, data uncertainties are assumed to be the main cause for imbalances. The N and P SFAs presented in this study, as well as the derived recycling potentials, should be considered as estimates. It is strongly recommended to conduct a sampling campaign and use own measurements to correct these results.

Contribution to the Chinese national and regional political goals towards a sustainable agriculture

The results suggest that, combining the already recycled streams with the currently unutilized rotten tangerines and water bamboo as well as the resulting excreta from consumption, over 1,503 Mg N/a and 316 Mg P/a (725 Mg P 2 O 5 /a) could theoretically be recovered in Huangyan. Recovering these nutrients would allow a growth of agricultural production of 15% (based on N) and 13% (based on P), while fulfilling the zero-growth action plan of the Chinese government. Upscaling these results from Huangyan district to the region of Taizhou, 11,065 Mg N/a and 1,329 Mg P/a (3,043 Mg P 2 O 5 ) could theoretically be recovered (based on the production numbers for tangerines and water bamboo published in Taizhou’s statistical yearbook) [ 60 ]. Adding up the nutrient mass for N and P 2 O 5 then results in 14,108 Mg nutrients/a. This would exceed the goal of chemical fertilizer reduction (1,182 Mg of nutrients) by almost 12 times. It is worth mentioning that this result would be even better if potassium flows would have also been accounted for. Considering the negative environmental impacts caused by the utilization of chemical fertilizers [ 61 , 62 ], recycling activities can help to enhance environmental sustainability and support China in becoming carbon neutral in 2060.

Challenges and measures for practical implementation of nutrient recovery

While this study calculates the theoretical potential for nutrient recovery, several practical challenges must be addressed to enhance feasibility. Primarily, technical barriers exist, such as the efficiency of recovery technologies. For example, net losses of 18% of N were reported during anaerobic digestion [ 63 ], and for composting they can reach up to 50% [ 64 ]. Besides, the agricultural by-products analyzed in this study are from plant origin, and an addition of animal manure (which could imply a collaboration with other stakeholders) might be required to improve the efficiency of the recovery process. These technologies depend on (in some cases advanced) infrastructure and expertise, requiring investment in training and capacity-building for local technicians and farmers. Economic constraints also play a significant role: the initial investment costs for installing nutrient recovery systems can be a big barrier. As a reference, a household-scale biogas digester in China costs between 368 and 792 USD [ 65 ]. To encourage adoption, financial incentives such as subsidies or low-interest loans could be provided.

An important condition for stakeholders to adopt technologies to treat organic wastes for bio-based fertilizers’ production is that there needs to be a market for those fertilizers. Users of organic fertilizers have high quality expectations (nutrient content, nutrient release rates, risk) [ 66 ]. Moreover, a Chinese study on barriers to replace mineral fertilizers with manure showed that farmers have an overall negative attitude, lack of knowledge, and limited experience [ 67 ]. Targeted marketing strategies that provide information on the benefits and costs of implementation are needed, as well as regulatory tools that ensure price stability (to maximise the market share of these fertilizers, they should be 30–46% cheaper than equivalent mineral fertilizers) [ 68 ]. Sutton et al. [ 7 ] stress the importance of a holistic approach to nutrient management, advocating for improved nutrient use efficiency throughout the entire food chain to enhance food and energy production while minimizing losses that cause environmental impacts.

This study quantifies untapped theoretical recycling potentials for N and P throughout the tangerine and water bamboo life cycle in Huangyan, China in 2019 (370 ± 47 Mg N and 24 ± 3 Mg P for tangerines, and 384 ± 136 Mg N and 81 ± 29 Mg P for water bamboo). Hotspots for nutrient recovery include inefficient agricultural residue utilization, low recovery of nutrients from organic residues in municipal solid wastes (most N and P is landfilled), and missing recovery of N and P during wastewater treatment. N and P imports of 427 ± 128 Mg/a for tangerines and water bamboo production are contrasted by N and P exports of 2,189 ± 560 Mg/a. Such imbalances are symptomatic for cash crop producing regions and result in the need of chemical fertilizer imports. Implementing circular economy management approaches such as precision farming, source waste separation, composting, or anaerobic digestion, combined with advanced wastewater treatment concepts could improve N and P recovery.

The recovery of these nutrients could substitute 59% of N and 15% of P supplied by chemical fertilizers for tangerines and water bamboo production in Huangyan, contributing to the circular economy and the achievement of political goals in Taizhou and China. Using untapped nutrients enables further production growth while reducing chemical fertilizer application, contributing to the zero-growth action plan of the Chinese Ministry of Agriculture. The use of organic fertilizers from agricultural residues and municipal solid waste and wastewater allows low-carbon agriculture and improvement of the utilization level of agricultural resources in line with the 14th 5-year plan of the Chinese government, paving the path towards carbon neutrality in 2060. On a regional level, implementing these circular concepts would allow Taizhou to reach the goal of increasing the use of organic fertilizer, digestate from anaerobic digestion, and green manure; improving soil structure and organic matter content. Taizhou could exceed the expected nutrients saving of 0.6 kg (sum of N, P 2 O 5 and K 2 O) per Mu—or more than 1,000 Mg per year (worth over 5 million yuan)—reducing air pollution (mainly caused by straw burning), eutrophication of water bodies, soil erosion and salinization.

Reliable data are crucial for potential assessments, yet currently available Chinese data for regional material and substance flows stems from statistical yearbooks, which lack scientific basis. To address this uncertain data foundation, this study defines data representativeness levels. This enables a first quantification and visualization and supports the identification of data weak points for future studies to address. The study identified theoretical recycling potentials, but several challenges related to technology efficiencies, costs, and users’ acceptance need to be addressed to ensure feasibility.

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We gratefully acknowledge the support of the Open Access Publication Fund of the Technische Universität Berlin.

Open Access funding enabled and organized by Projekt DEAL. This research was funded by the German Ministry for Research and Education (BMBF) in the context of the research and development project Urban–Rural Assembly (URA)–Managing inclusive transformation-to-sustainability processes at the urban–rural interface of the Huangyan-Taizhou region in China (Grant No. 01LE1804A). Julia Santolin is a holder of a Ph.D. fellowship strategic basic research from the Research Foundation—Flanders (Grant No. 1S57222N).

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Santolin, J., Larsen, O.C., Fritze, A. et al. Reaching China’s fertilizer reduction goals through nitrogen and phosphorus recovery: a substance flow analysis case study. J Mater Cycles Waste Manag (2024). https://doi.org/10.1007/s10163-024-02067-6

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Abstract: 3D face reconstruction (3DFR) algorithms are based on specific assumptions tailored to distinct application scenarios. These assumptions limit their use when acquisition conditions, such as the subject's distance from the camera or the camera's characteristics, are different than expected, as typically happens in video surveillance. Additionally, 3DFR algorithms follow various strategies to address the reconstruction of a 3D shape from 2D data, such as statistical model fitting, photometric stereo, or deep learning. In the present study, we explore the application of three 3DFR algorithms representative of the SOTA, employing each one as the template set generator for a face verification system. The scores provided by each system are combined by score-level fusion. We show that the complementarity induced by different 3DFR algorithms improves performance when tests are conducted at never-seen-before distances from the camera and camera characteristics (cross-distance and cross-camera settings), thus encouraging further investigations on multiple 3DFR-based approaches.

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