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Research Guides

Multiple Case Studies

Nadia Alqahtani and Pengtong Qu

Description

The case study approach is popular across disciplines in education, anthropology, sociology, psychology, medicine, law, and political science (Creswell, 2013). It is both a research method and a strategy (Creswell, 2013; Yin, 2017). In this type of research design, a case can be an individual, an event, or an entity, as determined by the research questions. There are two variants of the case study: the single-case study and the multiple-case study. The former design can be used to study and understand an unusual case, a critical case, a longitudinal case, or a revelatory case. On the other hand, a multiple-case study includes two or more cases or replications across the cases to investigate the same phenomena (Lewis-Beck, Bryman & Liao, 2003; Yin, 2017). …a multiple-case study includes two or more cases or replications across the cases to investigate the same phenomena

The difference between the single- and multiple-case study is the research design; however, they are within the same methodological framework (Yin, 2017). Multiple cases are selected so that “individual case studies either (a) predict similar results (a literal replication) or (b) predict contrasting results but for anticipatable reasons (a theoretical replication)” (p. 55). When the purpose of the study is to compare and replicate the findings, the multiple-case study produces more compelling evidence so that the study is considered more robust than the single-case study (Yin, 2017).

To write a multiple-case study, a summary of individual cases should be reported, and researchers need to draw cross-case conclusions and form a cross-case report (Yin, 2017). With evidence from multiple cases, researchers may have generalizable findings and develop theories (Lewis-Beck, Bryman & Liao, 2003).

Creswell, J. W. (2013). Qualitative inquiry and research design: Choosing among five approaches (3rd ed.). Los Angeles, CA: Sage.

Lewis-Beck, M., Bryman, A. E., & Liao, T. F. (2003). The Sage encyclopedia of social science research methods . Los Angeles, CA: Sage.

Yin, R. K. (2017). Case study research and applications: Design and methods . Los Angeles, CA: Sage.

Key Research Books and Articles on Multiple Case Study Methodology

Yin discusses how to decide if a case study should be used in research. Novice researchers can learn about research design, data collection, and data analysis of different types of case studies, as well as writing a case study report.

Chapter 2 introduces four major types of research design in case studies: holistic single-case design, embedded single-case design, holistic multiple-case design, and embedded multiple-case design. Novice researchers will learn about the definitions and characteristics of different designs. This chapter also teaches researchers how to examine and discuss the reliability and validity of the designs.

Creswell, J. W., & Poth, C. N. (2017). Qualitative inquiry and research design: Choosing among five approaches . Los Angeles, CA: Sage.

This book compares five different qualitative research designs: narrative research, phenomenology, grounded theory, ethnography, and case study. It compares the characteristics, data collection, data analysis and representation, validity, and writing-up procedures among five inquiry approaches using texts with tables. For each approach, the author introduced the definition, features, types, and procedures and contextualized these components in a study, which was conducted through the same method. Each chapter ends with a list of relevant readings of each inquiry approach.

This book invites readers to compare these five qualitative methods and see the value of each approach. Readers can consider which approach would serve for their research contexts and questions, as well as how to design their research and conduct the data analysis based on their choice of research method.

Günes, E., & Bahçivan, E. (2016). A multiple case study of preservice science teachers’ TPACK: Embedded in a comprehensive belief system. International Journal of Environmental and Science Education, 11 (15), 8040-8054.

In this article, the researchers showed the importance of using technological opportunities in improving the education process and how they enhanced the students’ learning in science education. The study examined the connection between “Technological Pedagogical Content Knowledge” (TPACK) and belief system in a science teaching context. The researchers used the multiple-case study to explore the effect of TPACK on the preservice science teachers’ (PST) beliefs on their TPACK level. The participants were three teachers with the low, medium, and high level of TPACK confidence. Content analysis was utilized to analyze the data, which were collected by individual semi-structured interviews with the participants about their lesson plans. The study first discussed each case, then compared features and relations across cases. The researchers found that there was a positive relationship between PST’s TPACK confidence and TPACK level; when PST had higher TPACK confidence, the participant had a higher competent TPACK level and vice versa.

Recent Dissertations Using Multiple Case Study Methodology

Milholland, E. S. (2015). A multiple case study of instructors utilizing Classroom Response Systems (CRS) to achieve pedagogical goals . Retrieved from ProQuest Dissertations & Theses Global. (Order Number 3706380)

The researcher of this study critiques the use of Classroom Responses Systems by five instructors who employed this program five years ago in their classrooms. The researcher conducted the multiple-case study methodology and categorized themes. He interviewed each instructor with questions about their initial pedagogical goals, the changes in pedagogy during teaching, and the teaching techniques individuals used while practicing the CRS. The researcher used the multiple-case study with five instructors. He found that all instructors changed their goals during employing CRS; they decided to reduce the time of lecturing and to spend more time engaging students in interactive activities. This study also demonstrated that CRS was useful for the instructors to achieve multiple learning goals; all the instructors provided examples of the positive aspect of implementing CRS in their classrooms.

Li, C. L. (2010). The emergence of fairy tale literacy: A multiple case study on promoting critical literacy of children through a juxtaposed reading of classic fairy tales and their contemporary disruptive variants . Retrieved from ProQuest Dissertations & Theses Global. (Order Number 3572104)

To explore how children’s development of critical literacy can be impacted by their reactions to fairy tales, the author conducted a multiple-case study with 4 cases, in which each child was a unit of analysis. Two Chinese immigrant children (a boy and a girl) and two American children (a boy and a girl) at the second or third grade were recruited in the study. The data were collected through interviews, discussions on fairy tales, and drawing pictures. The analysis was conducted within both individual cases and cross cases. Across four cases, the researcher found that the young children’s’ knowledge of traditional fairy tales was built upon mass-media based adaptations. The children believed that the representations on mass-media were the original stories, even though fairy tales are included in the elementary school curriculum. The author also found that introducing classic versions of fairy tales increased children’s knowledge in the genre’s origin, which would benefit their understanding of the genre. She argued that introducing fairy tales can be the first step to promote children’s development of critical literacy.

Asher, K. C. (2014). Mediating occupational socialization and occupational individuation in teacher education: A multiple case study of five elementary pre-service student teachers . Retrieved from ProQuest Dissertations & Theses Global. (Order Number 3671989)

This study portrayed five pre-service teachers’ teaching experience in their student teaching phase and explored how pre-service teachers mediate their occupational socialization with occupational individuation. The study used the multiple-case study design and recruited five pre-service teachers from a Midwestern university as five cases. Qualitative data were collected through interviews, classroom observations, and field notes. The author implemented the case study analysis and found five strategies that the participants used to mediate occupational socialization with occupational individuation. These strategies were: 1) hindering from practicing their beliefs, 2) mimicking the styles of supervising teachers, 3) teaching in the ways in alignment with school’s existing practice, 4) enacting their own ideas, and 5) integrating and balancing occupational socialization and occupational individuation. The study also provided recommendations and implications to policymakers and educators in teacher education so that pre-service teachers can be better supported.

Multiple Case Studies Copyright © 2019 by Nadia Alqahtani and Pengtong Qu is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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Perspectives from Researchers on Case Study Design

by Janet Salmons, PhD, Research Community Manager for SAGE Methodspace

Research design is the focus for the first quarter of 2023. Find a post about case study design , and read the unfolding series of posts here .

What is a “case study” research design?

Linda Bloomberg describes a case study as:

An in-depth exploration from multiple perspectives of the richness and complexity of a particular social unit, system, or phenomenon. Its primary purpose is to generate understanding and insights in order to gain knowledge and inform professional practice, policy development, and community or social action. Case study research is typically extensive; it draws on multiple methods of data collection and involves multiple data sources.

The researcher begins by identifying a specific case or set of cases to be studied. Each case is an entity that is described within certain parameters, such as a specific time frame, place, event, and process. Hence, the case becomes a bounded system . Typically, case study researchers analyze the real-life cases that are currently in progress so that they can gather accurate information that is not lost by time.

This method culminates in the production of a detailed description of a setting and its participants, accompanied by an analysis of the data for themes, patterns, and issues. A case study is therefore both a process of inquiry about the case at hand and the product of that inquiry. (Bloomberg, 2018, p. 276)

Case studies use more than one form of data either within a research paradigm (multimodal ), or more than one form of data from different paradigms (mixed methods). As Bloomberg notes, the case study method is employed across disciplines, including education, health care, social work, history, sociology, management studies, and organizational studies. When you look at lists of most-read and most-cited articles you will find that this flexible approach is widely used and published. Here are some open-access articles about multimodal qualitative or mixed methods designs that include both qualitative and quantitative elements.

Qualitative Research with Case Studies

Brannen, J., & Nilsen, A. (2011). Comparative Biographies in Case-based Cross-national Research: Methodological Considerations. Sociology, 45(4), 603–618. https://doi.org/10.1177/0038038511406602

Abstract. This article examines some methodological issues relating to an embedded case study design adopted in a comparative cross-national study of working parents covering three levels of social context: the macro level; the workplace level; and the individual level. It addresses issues of generalizability, in particular the importance of criteria for the selection of cases in the research design and analysis phases. To illustrate the benefits of the design the article focuses on the level of individual biographies. Three exemplars of biographical trajectories and experiences are presented and discussed. It is argued that a multi-tiered design and a comparative biographical approach can add to the understanding of individual experience by placing it in context and thus yield knowledge that is of general sociological relevance by demonstrating the interrelatedness of agency and structure.

Ebneyamini, S., & Sadeghi Moghadam, M. R. (2018). Toward Developing a Framework for Conducting Case Study Research. International Journal of Qualitative Methods, 17(1). https://doi.org/10.1177/1609406918817954

Abstract. This article reviews the use of case study research for both practical and theoretical issues especially in management field with the emphasis on management of technology and innovation. Many researchers commented on the methodological issues of the case study research from their point of view thus, presenting a comprehensive framework was missing. We try representing a general framework with methodological and analytical perspective to design, develop, and conduct case study research. To test the coverage of our framework, we have analyzed articles in three major journals related to the management of technology and innovation to approve our framework. This study represents a general structure to guide, design, and fulfill a case study research with levels and steps necessary for researchers to use in their research.

Flyvbjerg, B. (2006). Five Misunderstandings About Case-Study Research. Qualitative Inquiry, 12(2), 219–245. https://doi.org/10.1177/1077800405284363

Abstract. This article examines five common misunderstandings about case-study research: (a) theoretical knowledge is more valuable than practical knowledge; (b) one cannot generalize from a single case, therefore, the single-case study cannot contribute to scientific development; (c) the case study is most useful for generating hypotheses, whereas other methods are more suitable for hypotheses testing and theory building; (d) the case study contains a bias toward verification; and (e) it is often difficult to summarize specific case studies. This article explains and corrects these misunderstandings one by one and concludes with the Kuhnian insight that a scientific discipline without a large number of thoroughly executed case studies is a discipline without systematic production of exemplars, and a discipline without exemplars is an ineffective one. Social science may be strengthened by the execution of a greater number of good case studies.

Morgan SJ, Pullon SRH, Macdonald LM, McKinlay EM, Gray BV. Case Study Observational Research: A Framework for Conducting Case Study Research Where Observation Data Are the Focus. Qualitative Health Research. 2017;27(7):1060-1068. doi:10.1177/1049732316649160

Abstract. Case study research is a comprehensive method that incorporates multiple sources of data to provide detailed accounts of complex research phenomena in real-life contexts. However, current models of case study research do not particularly distinguish the unique contribution observation data can make. Observation methods have the potential to reach beyond other methods that rely largely or solely on self-report. This article describes the distinctive characteristics of case study observational research, a modified form of Yin’s 2014 model of case study research the authors used in a study exploring interprofessional collaboration in primary care. In this approach, observation data are positioned as the central component of the research design. Case study observational research offers a promising approach for researchers in a wide range of health care settings seeking more complete understandings of complex topics, where contextual influences are of primary concern. Future research is needed to refine and evaluate the approach.

Rule, P., & John, V. M. (2015). A Necessary Dialogue: Theory in Case Study Research. International Journal of Qualitative Methods , 14 (4). https://doi.org/10.1177/1609406915611575

Abstract. This article is premised on the understanding that there are multiple dimensions of the case–theory relation and examines four of these: theory of the case, theory for the case, theory from the case, and a dialogical relation between theory and case. This fourth dimension is the article’s key contribution to theorizing case study. Dialogic engagement between theory and case study creates rich potential for mutual formation and generative tension. The article argues that the process of constructing and conducting the case is theory laden, while the outcomes of the study might also have theoretical implications. Case study research that is contextually sensitive and theoretically astute can contribute not only to the application and revision of existing theory but also to the development of new theory. The case thus provides a potentially generative nexus for the engagement of theory, context, and research.

Thomas, G. (2011). A Typology for the Case Study in Social Science Following a Review of Definition, Discourse, and Structure. Qualitative Inquiry, 17(6), 511–521. https://doi.org/10.1177/1077800411409884

Abstract. The author proposes a typology for the case study following a definition wherein various layers of classificatory principle are disaggregated. First, a clear distinction is drawn between two parts: (1) the subject of the study, which is the case itself, and (2) the object, which is the analytical frame or theory through which the subject is viewed and which the subject explicates. Beyond this distinction the case study is presented as classifiable by its purposes and the approaches adopted— principally with a distinction drawn between theory-centered and illustrative study. Beyond this, there are distinctions to be drawn among various operational structures that concern comparative versus noncomparative versions of the form and the ways that the study may employ time. The typology reveals that there are numerous valid permutations of these dimensions and many trajectories, therefore, open to the case inquirer.

VanWynsberghe, R., & Khan, S. (2007). Redefining Case Study. International Journal of Qualitative Methods , 6 (2), 80–94. https://doi.org/10.1177/160940690700600208

Abstract. In this paper the authors propose a more precise and encompassing definition of case study than is usually found. They support their definition by clarifying that case study is neither a method nor a methodology nor a research design as suggested by others. They use a case study prototype of their own design to propose common properties of case study and demonstrate how these properties support their definition. Next, they present several living myths about case study and refute them in relation to their definition. Finally, they discuss the interplay between the terms case study and unit of analysis to further delineate their definition of case study. The target audiences for this paper include case study researchers, research design and methods instructors, and graduate students interested in case study research.

Mixed Methods Research with Case Studies

Guetterman, T. C., & Fetters, M. D. (2018). Two Methodological Approaches to the Integration of Mixed Methods and Case Study Designs: A Systematic Review. American Behavioral Scientist, 62(7), 900–918. https://doi.org/10.1177/0002764218772641

Abstract. Case study has a tradition of collecting multiple forms of data—qualitative and quantitative—to gain a more complete understanding of the case. Case study integrates well with mixed methods, which seeks a more complete understanding through the integration of qualitative and quantitative research. We identify and characterize “mixed methods–case study designs” as mixed methods studies with a nested case study and “case study–mixed methods designs” as case studies with nested mixed methods. Based on a review of published research integrating mixed methods and case study designs, we describe key methodological features and discuss four exemplar interdisciplinary studies.

Luyt, R. (2012). A Framework for Mixing Methods in Quantitative Measurement Development, Validation, and Revision: A Case Study. Journal of Mixed Methods Research, 6(4), 294–316. https://doi.org/10.1177/1558689811427912

Abstract. A framework for quantitative measurement development, validation, and revision that incorporates both qualitative and quantitative methods is introduced. It extends and adapts Adcock and Collier’s work, and thus, facilitates understanding of quantitative measurement development, validation, and revision as an integrated and cyclical set of procedures best achieved through mixed methods research. It also offers a systematic guide concerning how these procedures may be undertaken through detailing key “stages,” “levels,” and practical “tasks.” A case study illustrates how qualitative and quantitative methods may be mixed through the use of the proposed framework in the cross-cultural content- and construct-related validation and subsequent revision of a quantitative measure. The contribution of this article to mixed methods research literature is briefly discussed.

Mason, W., Morris, K., Webb, C., Daniels, B., Featherstone, B., Bywaters, P., Mirza, N., Hooper, J., Brady, G., Bunting, L., & Scourfield, J. (2020). Toward Full Integration of Quantitative and Qualitative Methods in Case Study Research: Insights From Investigating Child Welfare Inequalities. Journal of Mixed Methods Research, 14(2), 164–183. https://doi.org/10.1177/1558689819857972

Abstract. Delineation of the full integration of quantitative and qualitative methods throughout all stages of multisite mixed methods case study projects remains a gap in the methodological literature. This article offers advances to the field of mixed methods by detailing the application and integration of mixed methods throughout all stages of one such project; a study of child welfare inequalities. By offering a critical discussion of site selection and the management of confirmatory, expansionary and discordant data, this article contributes to the limited body of mixed methods exemplars specific to this field. We propose that our mixed methods approach provided distinctive insights into a complex social problem, offering expanded understandings of the relationship between poverty, child abuse, and neglect.

Onghena, P., Maes, B., & Heyvaert, M. (2019). Mixed Methods Single Case Research: State of the Art and Future Directions. Journal of Mixed Methods Research, 13(4), 461–480. https://doi.org/10.1177/1558689818789530

Abstract. Mixed methods single case research (MMSCR) is research in which single case experimental and qualitative case study methodologies, and their accompanying sets of methods and techniques, are integrated to answer research questions that concern a single case. This article discusses the historical roots and the distinct nature of MMSCR, the kinds of knowledge MMSCR produces, its philosophical underpinnings, examples of MMSCR, and the trustworthiness and validity of MMSCR. Methodological challenges relate to the development of a critical appraisal tool for MMSCR, to the team work that is involved in designing and conducting MMSCR studies, and to the application of mixed methods research synthesis for multiple case studies and single case experiments.

Sharp, J. L., Mobley, C., Hammond, C., Withington, C., Drew, S., Stringfield, S., & Stipanovic, N. (2012). A Mixed Methods Sampling Methodology for a Multisite Case Study. Journal of Mixed Methods Research, 6(1), 34–54. https://doi.org/10.1177/1558689811417133

Abstract. The flexibility of mixed methods research strategies makes such approaches especially suitable for multisite case studies. Yet the utilization of mixed methods to select sites for these studies is rarely reported. The authors describe their pragmatic mixed methods approach to select a sample for their multisite mixed methods case study of a statewide education policy initiative in the United States. The authors designed a four-stage sequential mixed methods site selection strategy to select eight sites in order to capture the broader context of the research, as well as any contextual nuances that shape policy implementation. The authors anticipate that their experience would provide guidance to other mixed methods researchers seeking to maximize the rigor of their multisite case study sampling designs.

Bloomberg, L. (2018). Case study. In B. B. Frey (Ed.), The SAGE encyclopedia of educational research, measurement, and evaluation . https://doi.org/10.4135/9781506326139

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Case Study – Methods, Examples and Guide

Table of Contents

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.

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Questionnaire – Definition, Types, and Examples

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Qualitative Research Methods

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Methodology: Multiple-Case Qualitative Study

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This longitudinal multiple-case study is qualitative in nature, with data collection lasting for more than a year. As this study set out to understand the experiences, feelings, emotions, conceptions, and understanding of students about their experiences, a qualitative research approach was adopted to “identify issues from the perspective of” the participants, and to study them in a natural setting (Hennink et al., 2011, p. 9).

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5 Benefits of Learning Through the Case Study Method

Harvard Business School MBA students learning through the case study method

28 Nov 2023

While several factors make HBS Online unique —including a global Community and real-world outcomes —active learning through the case study method rises to the top.

In a 2023 City Square Associates survey, 74 percent of HBS Online learners who also took a course from another provider said HBS Online’s case method and real-world examples were better by comparison.

Here’s a primer on the case method, five benefits you could gain, and how to experience it for yourself.

Access your free e-book today.

What Is the Harvard Business School Case Study Method?

The case study method , or case method , is a learning technique in which you’re presented with a real-world business challenge and asked how you’d solve it. After working through it yourself and with peers, you’re told how the scenario played out.

HBS pioneered the case method in 1922. Shortly before, in 1921, the first case was written.

“How do you go into an ambiguous situation and get to the bottom of it?” says HBS Professor Jan Rivkin, former senior associate dean and chair of HBS's master of business administration (MBA) program, in a video about the case method . “That skill—the skill of figuring out a course of inquiry to choose a course of action—that skill is as relevant today as it was in 1921.”

Originally developed for the in-person MBA classroom, HBS Online adapted the case method into an engaging, interactive online learning experience in 2014.

In HBS Online courses , you learn about each case from the business professional who experienced it. After reviewing their videos, you’re prompted to take their perspective and explain how you’d handle their situation.

You then get to read peers’ responses, “star” them, and comment to further the discussion. Afterward, you learn how the professional handled it and their key takeaways.

HBS Online’s adaptation of the case method incorporates the famed HBS “cold call,” in which you’re called on at random to make a decision without time to prepare.

“Learning came to life!” said Sheneka Balogun , chief administration officer and chief of staff at LeMoyne-Owen College, of her experience taking the Credential of Readiness (CORe) program . “The videos from the professors, the interactive cold calls where you were randomly selected to participate, and the case studies that enhanced and often captured the essence of objectives and learning goals were all embedded in each module. This made learning fun, engaging, and student-friendly.”

If you’re considering taking a course that leverages the case study method, here are five benefits you could experience.

5 Benefits of Learning Through Case Studies

1. take new perspectives.

The case method prompts you to consider a scenario from another person’s perspective. To work through the situation and come up with a solution, you must consider their circumstances, limitations, risk tolerance, stakeholders, resources, and potential consequences to assess how to respond.

Taking on new perspectives not only can help you navigate your own challenges but also others’. Putting yourself in someone else’s situation to understand their motivations and needs can go a long way when collaborating with stakeholders.

2. Hone Your Decision-Making Skills

Another skill you can build is the ability to make decisions effectively . The case study method forces you to use limited information to decide how to handle a problem—just like in the real world.

Throughout your career, you’ll need to make difficult decisions with incomplete or imperfect information—and sometimes, you won’t feel qualified to do so. Learning through the case method allows you to practice this skill in a low-stakes environment. When facing a real challenge, you’ll be better prepared to think quickly, collaborate with others, and present and defend your solution.

3. Become More Open-Minded

As you collaborate with peers on responses, it becomes clear that not everyone solves problems the same way. Exposing yourself to various approaches and perspectives can help you become a more open-minded professional.

When you’re part of a diverse group of learners from around the world, your experiences, cultures, and backgrounds contribute to a range of opinions on each case.

On the HBS Online course platform, you’re prompted to view and comment on others’ responses, and discussion is encouraged. This practice of considering others’ perspectives can make you more receptive in your career.

“You’d be surprised at how much you can learn from your peers,” said Ratnaditya Jonnalagadda , a software engineer who took CORe.

In addition to interacting with peers in the course platform, Jonnalagadda was part of the HBS Online Community , where he networked with other professionals and continued discussions sparked by course content.

“You get to understand your peers better, and students share examples of businesses implementing a concept from a module you just learned,” Jonnalagadda said. “It’s a very good way to cement the concepts in one's mind.”

4. Enhance Your Curiosity

One byproduct of taking on different perspectives is that it enables you to picture yourself in various roles, industries, and business functions.

“Each case offers an opportunity for students to see what resonates with them, what excites them, what bores them, which role they could imagine inhabiting in their careers,” says former HBS Dean Nitin Nohria in the Harvard Business Review . “Cases stimulate curiosity about the range of opportunities in the world and the many ways that students can make a difference as leaders.”

Through the case method, you can “try on” roles you may not have considered and feel more prepared to change or advance your career .

5. Build Your Self-Confidence

Finally, learning through the case study method can build your confidence. Each time you assume a business leader’s perspective, aim to solve a new challenge, and express and defend your opinions and decisions to peers, you prepare to do the same in your career.

According to a 2022 City Square Associates survey , 84 percent of HBS Online learners report feeling more confident making business decisions after taking a course.

“Self-confidence is difficult to teach or coach, but the case study method seems to instill it in people,” Nohria says in the Harvard Business Review . “There may well be other ways of learning these meta-skills, such as the repeated experience gained through practice or guidance from a gifted coach. However, under the direction of a masterful teacher, the case method can engage students and help them develop powerful meta-skills like no other form of teaching.”

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No matter which course or credential program you choose, you’ll examine case studies from real business professionals, work through their challenges alongside peers, and gain valuable insights to apply to your career.

Are you interested in discovering how HBS Online can help advance your career? Explore our course catalog and download our free guide —complete with interactive workbook sections—to determine if online learning is right for you and which course to take.

About the Author

Research Design Review

A discussion of qualitative & quantitative research design, a multi-method approach in qualitative research.

A portion of the following is taken from Applied Qualitative Research Design: A Total Quality Framework Approach (Roller & Lavrakas, 2015, pp. 288-289).

Qualitative multi-method research—due to the additional data collection and analysis considerations—has the potential disadvantage of consuming valuable resources such as time and available research funds. However, this is not always the case and, under the appropriate conditions, multiple qualitative methods can prove very useful toward gaining a more fully developed complexity and meaning in the researcher’s understanding of a subject matter compared to a single-method research design (cf. Denzin & Lincoln, 2011; Flick, 2007).

Ethnography is one such example. Observation is the principal method in an ethnographic study; however, it is often supplemented with other qualitative methods such as in-depth interviews (IDIs), focus group discussions, and/or documentary review in order to provide a more complete “picture” of the issue or phenomenon under investigation. Other applications of multi-method qualitative research are not uncommon. Lambert and Loiselle (2008), for instance, combined focus group discussions and IDIs in a study with cancer patients concerning their “information-seeking behavior.” These researchers found that this multi-method approach enriched the study because one method helped inform the other—for example, group discussions identified relevant questions/issues that were then used in the IDIs—and contributed unique information—for example, the IDIs were effective in obtaining details of patients’ information-seeking processes—as well as contextual clarification—for example, the focus groups were more valuable in highlighting contextual influences on these processes such as the physicians’ preferences or recommendations. Lambert and Loiselle concluded that the multi-method research design “enhanced understanding of the structure and essential characteristics of the phenomenon within the context of cancer” (p. 235).

Research Design Review has published articles on two special types of multiple-method qualitative research— case study and narrative research —each of which is a form of “case-centered” qualitative research, a term coined by Mishler (1996, 1999) and used by others (cf. Riessman, 2008) to denote a research approach that preserves the “unity and coherence” of the research subject throughout data collection and analysis. A six-step approach to case-centered research design is discussed in this article .

Regardless of the particular multi-method design or type of research, a multiple-method approach requires a unique set of qualitative researcher skills. These skills are discussed in this article— “Working with Multiple Methods in Qualitative Research: 7 Unique Researcher Skills.”

Brewer, J., & Hunter, A. (2006). Foundations of multimethod research: Synthesizing styles . Thousand Oaks, CA: Sage Publications.

Denzin, N. K., & Lincoln, Y. S. (Eds.). (2011). The Sage handbook of qualitative research . Thousand Oaks, CA: Sage Publications.

Flick, U. (2007). Designing qualitative research . London: Sage Publications.

Lambert, S. D., & Loiselle, C. G. (2008). Combining individual interviews and focus groups to enhance data richness. Journal of Advanced Nursing , 62 (2), 228–237. https://doi.org/10.1111/j.1365-2648.2007.04559.x

Mishler, E. G. (1996). Missing persons: Recovering developmental stories/histories. In R. Jessor, A. Colby, & R. A. Shweder (Eds.), Ethnography and human development: Context and meaning in social inquiry (pp. 73–100). Chicago, IL: The University of Chicago Press.

Mishler, E. G. (1999). Storylines: Craftartitists’ narratives of identity . Cambridge, MA: Harvard University Press.

Riessman, C. K. (2008). Narrative methods for the human sciences . Thousand Oaks, CA: Sage Publications.

Snape, D., & Spencer, L. (2003). The foundations of qualitative research. In J. Ritchie & J. Lewis (Eds.), Qualitative research practice . London: Sage Publications.

10 Case Study Advantages and Disadvantages

case study advantages and disadvantages, explained below

A case study in academic research is a detailed and in-depth examination of a specific instance or event, generally conducted through a qualitative approach to data.

The most common case study definition that I come across is is Robert K. Yin’s (2003, p. 13) quote provided below:

“An empirical inquiry that investigates a contemporary phenomenon within its real-life context, especially when the boundaries between phenomenon and context are not clearly evident.”

Researchers conduct case studies for a number of reasons, such as to explore complex phenomena within their real-life context, to look at a particularly interesting instance of a situation, or to dig deeper into something of interest identified in a wider-scale project.

While case studies render extremely interesting data, they have many limitations and are not suitable for all studies. One key limitation is that a case study’s findings are not usually generalizable to broader populations because one instance cannot be used to infer trends across populations.

Case Study Advantages and Disadvantages

1. in-depth analysis of complex phenomena.

Case study design allows researchers to delve deeply into intricate issues and situations.

By focusing on a specific instance or event, researchers can uncover nuanced details and layers of understanding that might be missed with other research methods, especially large-scale survey studies.

As Lee and Saunders (2017) argue,

“It allows that particular event to be studies in detail so that its unique qualities may be identified.”

This depth of analysis can provide rich insights into the underlying factors and dynamics of the studied phenomenon.

2. Holistic Understanding

Building on the above point, case studies can help us to understand a topic holistically and from multiple angles.

This means the researcher isn’t restricted to just examining a topic by using a pre-determined set of questions, as with questionnaires. Instead, researchers can use qualitative methods to delve into the many different angles, perspectives, and contextual factors related to the case study.

We can turn to Lee and Saunders (2017) again, who notes that case study researchers “develop a deep, holistic understanding of a particular phenomenon” with the intent of deeply understanding the phenomenon.

3. Examination of rare and Unusual Phenomena

We need to use case study methods when we stumble upon “rare and unusual” (Lee & Saunders, 2017) phenomena that would tend to be seen as mere outliers in population studies.

Take, for example, a child genius. A population study of all children of that child’s age would merely see this child as an outlier in the dataset, and this child may even be removed in order to predict overall trends.

So, to truly come to an understanding of this child and get insights into the environmental conditions that led to this child’s remarkable cognitive development, we need to do an in-depth study of this child specifically – so, we’d use a case study.

4. Helps Reveal the Experiences of Marginalzied Groups

Just as rare and unsual cases can be overlooked in population studies, so too can the experiences, beliefs, and perspectives of marginalized groups.

As Lee and Saunders (2017) argue, “case studies are also extremely useful in helping the expression of the voices of people whose interests are often ignored.”

Take, for example, the experiences of minority populations as they navigate healthcare systems. This was for many years a “hidden” phenomenon, not examined by researchers. It took case study designs to truly reveal this phenomenon, which helped to raise practitioners’ awareness of the importance of cultural sensitivity in medicine.

5. Ideal in Situations where Researchers cannot Control the Variables

Experimental designs – where a study takes place in a lab or controlled environment – are excellent for determining cause and effect . But not all studies can take place in controlled environments (Tetnowski, 2015).

When we’re out in the field doing observational studies or similar fieldwork, we don’t have the freedom to isolate dependent and independent variables. We need to use alternate methods.

Case studies are ideal in such situations.

A case study design will allow researchers to deeply immerse themselves in a setting (potentially combining it with methods such as ethnography or researcher observation) in order to see how phenomena take place in real-life settings.

6. Supports the generation of new theories or hypotheses

While large-scale quantitative studies such as cross-sectional designs and population surveys are excellent at testing theories and hypotheses on a large scale, they need a hypothesis to start off with!

This is where case studies – in the form of grounded research – come in. Often, a case study doesn’t start with a hypothesis. Instead, it ends with a hypothesis based upon the findings within a singular setting.

The deep analysis allows for hypotheses to emerge, which can then be taken to larger-scale studies in order to conduct further, more generalizable, testing of the hypothesis or theory.

7. Reveals the Unexpected

When a largescale quantitative research project has a clear hypothesis that it will test, it often becomes very rigid and has tunnel-vision on just exploring the hypothesis.

Of course, a structured scientific examination of the effects of specific interventions targeted at specific variables is extermely valuable.

But narrowly-focused studies often fail to shine a spotlight on unexpected and emergent data. Here, case studies come in very useful. Oftentimes, researchers set their eyes on a phenomenon and, when examining it closely with case studies, identify data and come to conclusions that are unprecedented, unforeseen, and outright surprising.

As Lars Meier (2009, p. 975) marvels, “where else can we become a part of foreign social worlds and have the chance to become aware of the unexpected?”

Disadvantages

1. not usually generalizable.

Case studies are not generalizable because they tend not to look at a broad enough corpus of data to be able to infer that there is a trend across a population.

As Yang (2022) argues, “by definition, case studies can make no claims to be typical.”

Case studies focus on one specific instance of a phenomenon. They explore the context, nuances, and situational factors that have come to bear on the case study. This is really useful for bringing to light important, new, and surprising information, as I’ve already covered.

But , it’s not often useful for generating data that has validity beyond the specific case study being examined.

2. Subjectivity in interpretation

Case studies usually (but not always) use qualitative data which helps to get deep into a topic and explain it in human terms, finding insights unattainable by quantitative data.

But qualitative data in case studies relies heavily on researcher interpretation. While researchers can be trained and work hard to focus on minimizing subjectivity (through methods like triangulation), it often emerges – some might argue it’s innevitable in qualitative studies.

So, a criticism of case studies could be that they’re more prone to subjectivity – and researchers need to take strides to address this in their studies.

3. Difficulty in replicating results

Case study research is often non-replicable because the study takes place in complex real-world settings where variables are not controlled.

So, when returning to a setting to re-do or attempt to replicate a study, we often find that the variables have changed to such an extent that replication is difficult. Furthermore, new researchers (with new subjective eyes) may catch things that the other readers overlooked.

Replication is even harder when researchers attempt to replicate a case study design in a new setting or with different participants.

Comprehension Quiz for Students

Question 1: What benefit do case studies offer when exploring the experiences of marginalized groups?

a) They provide generalizable data. b) They help express the voices of often-ignored individuals. c) They control all variables for the study. d) They always start with a clear hypothesis.

Question 2: Why might case studies be considered ideal for situations where researchers cannot control all variables?

a) They provide a structured scientific examination. b) They allow for generalizability across populations. c) They focus on one specific instance of a phenomenon. d) They allow for deep immersion in real-life settings.

Question 3: What is a primary disadvantage of case studies in terms of data applicability?

a) They always focus on the unexpected. b) They are not usually generalizable. c) They support the generation of new theories. d) They provide a holistic understanding.

Question 4: Why might case studies be considered more prone to subjectivity?

a) They always use quantitative data. b) They heavily rely on researcher interpretation, especially with qualitative data. c) They are always replicable. d) They look at a broad corpus of data.

Question 5: In what situations are experimental designs, such as those conducted in labs, most valuable?

a) When there’s a need to study rare and unusual phenomena. b) When a holistic understanding is required. c) When determining cause-and-effect relationships. d) When the study focuses on marginalized groups.

Question 6: Why is replication challenging in case study research?

a) Because they always use qualitative data. b) Because they tend to focus on a broad corpus of data. c) Due to the changing variables in complex real-world settings. d) Because they always start with a hypothesis.

Lee, B., & Saunders, M. N. K. (2017). Conducting Case Study Research for Business and Management Students. SAGE Publications.

Meir, L. (2009). Feasting on the Benefits of Case Study Research. In Mills, A. J., Wiebe, E., & Durepos, G. (Eds.). Encyclopedia of Case Study Research (Vol. 2). London: SAGE Publications.

Tetnowski, J. (2015). Qualitative case study research design. Perspectives on fluency and fluency disorders , 25 (1), 39-45. ( Source )

Yang, S. L. (2022). The War on Corruption in China: Local Reform and Innovation . Taylor & Francis.

Yin, R. (2003). Case Study research. Thousand Oaks, CA: Sage.

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Advantages of the multiple case series approach to the study of cognitive deficits in autism spectrum disorder

In the neuropsychological case series approach, tasks are administered that tap different cognitive domains, and differences within rather than across individuals are the basis for theorising; each individual is effectively their own control. This approach is a mainstay of cognitive neuropsychology, and is particularly suited to the study of populations with heterogeneous deficits. However it has very rarely been applied to the study of cognitive differences in autism spectrum disorder (ASD). Here, we investigate whether this approach can yield information beyond that given by the typical group study method, when applied to an ASD population. Twenty-one high-functioning adult ASD participants and 22 IQ, age, and gender-matched control participants were administered a large battery of neuropsychological tests that would represent a typical neuropsychological assessment for neurological patients in the United Kingdom. The data were analysed using both group and single-case study methods. The group analysis revealed a limited number of deficits, principally on tests with a large executive function component, with no impairment in more routine abilities such as basic attending, language and perception. Single-case study analysis proved more fruitful revealing evidence of considerable variation in abilities both between and within ASD participants. Both sub-normal and supra-normal performance were observed, with the most defining feature of the ASD group being this variability. We conclude that the use of group-level analysis alone in the study of cognitive deficits in ASD risks missing cognitive characteristics that may be vitally important both theoretically and clinically, and even may be misleading because of averaging artifact.

1. Introduction

The acquired cognitive deficits experienced by neurological patients are heterogeneous, since no two brains are exactly alike, and the damage to them will differ from individual to individual, and individuals will differ greatly in their pre-morbid characteristics. This fact led to the adoption, principally through the 1980s, of the neuropsychological single-case design, and became a mainstay of the field of cognitive neuropsychology. The principal aim of this field was to build models of how the normal cognitive system is organised (as opposed to linking particular domains of cognition or their disorders to brain structures). This approach has now been used to extend our understanding of brain–behaviour relationships in virtually all domains of cognition, including perception, memory, language, reading and writing, numeracy, and executive function, and there are key papers using the single-case study methodology in each of these areas that have revolutionized our understanding of how the supporting brain systems are organised (see e.g. Shallice & Evans, 1978 for review). The neuropsychological single-case method should not be confused with the principally descriptive case studies that have traditionally appeared in, for instance, neurology and psychiatry (although these have their own value). Neuropsychological case study is an empirical procedure whose starting points are particular deficits or symptoms displayed, and a model of how the relevant cognitive systems are organised. The investigation then proceeds through a series of stages that seek to isolate the precise processing locus underpinning the impairment, excluding as many other possibilities and potential artifacts as possible. The conclusion of the investigation might be, in theoretically oriented work, a challenge to the underlying cognitive model, or in clinically oriented work, a better understanding of the causes of the symptom. There are many expositions on, and justifications of, this now widely accepted method (e.g. Caramazza, 1986; Caramazza & McCloskey, 1988; Coltheart, 1984; Shallice and Evans, 1978 ), and the approach has also been applied to the understanding of cognitive deficits in populations other than neurological ones (e.g. schizophrenia; Shallice et al., 1991 ).

Another condition where applying a single-case study approach may prove particularly enlightening is autism spectrum disorder (ASD). ASD is a neurodevelopmental disorder affecting approximately 1.0% of the population ( Baird et al., 2006 ) and which presents with problems in social interaction, verbal and non-verbal communication difficulties and repetitive and stereotyped disturbances of behaviour.

Behavioural and genetic studies find that ASD is unlikely to involve just a single primary processing deficit and is more likely to be associated with a complex pattern of deficits across and within domains ( Happe, Ronald, & Plomin, 2006; Minshew, Goldstein, & Siegel, 1997 ). In addition, Newschaffer, Fallin, and Lee (2002) report that the large variety of neuropathological changes and variability observed across patients suggest that ASD is etiologically heterogeneous. Consistent with this suggestion, recent neuroimaging studies indicate an abnormal pattern of functional specialization in the brains of participants with ASD ( Gilbert, Meuwese, Towgood, Frith, & Burgess, 2009; Pierce, Muller, Ambrose, Allen, & Courchesne, 2001 ). If the processes by which distinct brain regions become specialized for specific functions are disrupted in ASD, this may lead to complex and idiosyncratic patterns of strengths and weaknesses in particular individuals ( Gilbert et al., 2009 ). In this case, neuropsychological approaches are required that capture the variability in cognitive performance that is likely to accompany such atypical brain organisation and etiological heterogeneity.

Neuropsychological studies investigating ASD have typically used group study designs to investigate cognitive impairments. These studies have revealed that individuals present with an uneven pattern of cognitive strengths and weaknesses ( Frith, 2003b ). The cognitive deficits may include, but are not limited to, poor language comprehension, problems with working memory, failure to use context to support memory, poor memory for complex visual information, difficulties with planning and sequencing, difficulties with set shifting and a range of difficulties with complex attention. Strengths have also often been noted on tests of spatial reasoning and abstract problem-solving, on tests of rote memory and on tests of focused attention ( Frith, 2003b, 2004 ).

However, there is considerable disagreement between neuropsychological studies. For example, Hill (2004) reviews the evidence on executive function in ASD and finds mixed results. Whilst findings regarding some domains of executive function, such as inhibition of a pre-potent response, have been found to be fairly consistent, findings within other components, such as planning and mental flexibility, have been much more inconsistent (e.g. Mari, Castiello, Marks, Marraffa, & Prior, 2003; Minshew, Goldstein, Muenz, & Payton, 1992; Ozonoff & Jensen, 1999 ). Similarly, support for the weak central coherence theory of autism is also equivocal ( Happé & Frith, 2006 ). From their review of over 50 studies Happé and Frith concluded that whilst there have been some consistent findings, particularly with tasks such as the block design and the embedded figures tasks, other tasks, such as the Navon figures ( Navon, 1977 ) and various visual illusion tasks have produced inconsistent and sometimes negative findings (e.g. Happe, 1996; Mottron, Burack, Stauder, & Robaey, 1999; Plaisted, Swettenham, & Rees, 1999; Ropar & Mitchell, 2001 ). Finally, a recent review by Willcutt, Sonuga-Barke, Nigg, and Sergeant (2008) also concluded that the neuropsychological etiologies of ASD are complex and multifactorial, with no single deficit sufficient to explain all cases.

Three main explanations can be offered for this observed disparity. Firstly, perhaps the basis for these inconsistent results is that the ASD diagnosis incorporates individuals who are highly variable in terms of their abilities and disabilities, or is composed of multiple distinct subgroups. This could in turn lead to significant population sampling differences across studies. Moreover there is the strong danger of an “averaging artifact” ( Shallice and Evans, 1978 ), where the pattern detected at a group level does not describe well any single member of the group. A second possible explanation is that the ASD diagnosis does define a group of individuals with a distinct pattern of strengths and deficits, but the deficit is such that it can cause different results according to prima facie relatively minor changes in administration or task formats. An explanation of this kind might for example be that the ASD participants do not use social cues in the testing session as well as controls, or perhaps that they have attentional perturbations that mean slight task administration differences have major effects on performance. This detection problem would likely be exacerbated if no one study administered a full range of tests that might help characterise the nature of this problem. A third possible explanation is that ASD causes impairments in sensory and other processes (e.g. language comprehension, perception, short-term attention). These in turn may then cause unpredictable impairments in tests aimed at measuring higher level tasks (e.g. problem-solving), depending on the low-level features of specific tasks (e.g. stimulus materials). Since tests of these more lower level processes have typically not been administered in ASD studies, these deficits are potentially not detected.

The current study therefore applied both a group and multiple single-case series methodology using a comprehensive battery of neuropsychological tests to interpret the patterns of cognitive strengths and weaknesses in ASD. We tested the hypotheses that (i) observed deficits in higher order cognitive tasks in the ASD group are independent of deficits on lower level processes such as language comprehension, visual perception and short-term attention; (ii) patterns of deficit will vary from individual to individual within the ASD group; (iii) that this varying pattern of deficits across individuals demonstrated by the single-case approach is not revealed using traditional group study-type analysis; and (iv) the single-case study analysis will reveal strengths not detected in the traditional group study analysis. In order to be conservative in our hypothesis testing, we restricted our study to those ASD individuals performing in the high-functioning range on standardized intelligence tests; individual differences are likely to be smaller in a group of this type compared with a more heterogeneous sample.

2.1. Participant population

Baseline characteristics for the ASD and control participants are presented in Table 1 . Participants were 21 adults (17 males, 4 females) with ASD, all of whom had a clinical diagnosis of Asperger's syndrome. Participants were selected if both their performance and verbal IQ quotients exceeded 85. IQ was measured with the full 11 subtest battery of the Wechsler Adult Intelligence Scale-Third Edition (WAIS-III; Wechsler, 1997 ).

Baseline characteristics of the study participants.

ASD participants had all previously received a clinical diagnosis of ASD. All ASD participants were also administered the Autism Diagnostic Observation Scale (ADOS; Lord et al., 2000 ). Participants were included in the study regardless of whether or not they received an Autism/Autism Spectrum diagnosis on the ADOS. In addition, ASD symptom presentation was measured using the Autism Spectrum Quotient (AQ; Baron-Cohen, Wheelwright, Skinner, Martin, & Clubley, 2001 ). Results for the ADOS and AQ are presented in Table 1 .

Twenty-two VIQ, PIQ, FSIQ, age and gender-matched controls were also included in the study. Independent t -tests (two-tailed) indicated no significant difference for age, gender, VIQ, PIQ and FSIQ. Moreover, p values for each of these variables were above the 0.50 mark recommended by Mervis and Klein-Tasman (2004) to show strong overlap between the distributions in each group.

2.2. Measures

A range of valid, reliable neuropsychological tests which are routinely used in standard United Kingdom clinical neuropsychological practice were selected to tap a broad range of general cognitive abilities as discussed in the following section. All tests were administered according to the procedures outlined in the relevant testing manuals and published papers and a fixed order of testing was used for all participants.

2.2.1. Language

The ability to comprehend language and understand instructions was assessed using the de Renzi Token Test Shortened Version which employs tokens of three different colours and three different shapes, presented in a random array. Participants were administered 15 complex but abstract commands involving these tokens ( Coughlan & Warrington, 1978 ). The McKenna Graded Naming Test ( McKenna & Warrington, 1980 ), a 30 item test which assesses the ability to name line drawings of objects of graded difficulty, was also administered.

2.2.2. Perception

Object and space perception abilities were assessed with the “Shape Detection”, “Incomplete Letters”, “Object Decision” and “Dot Counting” subtests from the Visual Object Space Perception Battery (VOSP; Warrington & James, 1991 ). The “Shape Detection” subtest simply measures participants’ ability to detect an “X” on a card with an all over speckled pattern, with half of the cards containing an embedded and degraded “X” and half not containing an “X”. On the “Incomplete Letters” subtest participants attempt to name a degraded letter of the alphabet. On the “Object Decision” subtest the participant is presented with 20 cards, each printed with four black shapes one of which is a silhouette of a real object and three of which are silhouettes of nonsense objects, and asked to name the real object. Finally on the “Dot Counting” subtest participants simply count the number of dots arranged on separate cards. Participants also completed the “Minimal Features” and “Overlapping Figures” subtests from the Birmingham Object Recognition Battery (BORB; Humphreys & Riddoch, 1993 ). In the “Minimal Features” subtest participants were presented with three different pictures on each of 25 trials. One was a picture of the target object taken from the standard viewpoint, one was a picture of the target object taken from an unusual viewpoint and the third was an object visually similar to the target object. The task of the participant was to select the two matching objects. In the “Overlapping Figures” subtest speeded identification of non-overlapping letters, geometric shapes and objects were compared to speeded identification of overlapping letters, geometric shapes and objects.

2.2.3. Memory

Verbal and visual memory was assessed with the “Story Recall” and “Figure Copy” subtests from the Adult Memory and Information Processing Battery (AMIPB; Coughlan & Hollows, 1985 ). On the “Story Recall” subtest participants are first read a short story of the type you may hear on the television/radio or read in a newspaper and then immediately, and after a delay of approximately 30 min, asked to freely recall the story. On the “Figure Copy” subtest participants are presented with a complex geometrical figure to copy and after completing this copy immediately, and after a delay of approximately 30 min, asked to freely recall the design. Participants also completed the full Doors and People battery ( Baddeley, Emslie, & Nimmo-Smith, 1994 ). The Doors and People battery consists of four subtests and is designed to assess visual and verbal learning, free recall and recognition. On the “People Test” participants are first required to learn four forename/surname pairs with the assistance of a coloured photograph and after a short delay are again asked to recall these names. In the “Doors Test” participants are presented with a set of 12 coloured photographs of doors to learn and then later presented with a forced choice recognition task. On the “Shapes Test” participants learn four geometrical designs by first copying them, and then are asked to recall these shapes immediately, and again after a short delay. Finally, on the “Names Test” participants are presented with 12 forename/surname pairs to learn and then later presented with a forced choice recognition task.

2.2.4. Executive function

Executive function was assessed with the “Zoo Map” and “Six Elements” subtests from the Behavioural Assessment of Dysexecutive Syndrome (BADS; Wilson, Alderman, Burgess, Emslie, & Evans, 1996 ), the Hayling and Brixton ( Burgess & Shallice, 1997 ), the “Proverbs” subtest from the Delis Kaplan Executive Function Scale (DKEFS; Delis, Kaplan, & Kramer, 2001 ), the Cognitive Estimation Test (CET; Shallice & Evans, 1978 ), the Modified Card Sorting Test (MCST; Nelson, 1976 ), Controlled Oral Word Fluency (COWA; Benton, 1968 ), Trail Making Test ( Reitan, 1958 ), and the “Information Processing Speed Parts A and B” subtests from the AMIPB ( Coughlan and Hollows, 1985 ).

From the BADS, the “Zoo Map” subtest assesses planning by asking participants to show how they would visit a series of designated locations on a copy of a map, whilst also following a number of specified rules. On the “Six Elements” subtest participants are required to plan and organise their time to complete at least some of each of six separate sub-tasks, whilst following predefined rules. The “Proverbs” subtest from the D-KEFS measures mental flexibility and the ability to think abstractly and consists of eight sayings each of which the participant must give a meaning for, first in a free inquiry format and second by selecting from four multiple choice options. The CET measures the ability to generate effective problem-solving strategies and participants are asked to estimate answers to 10 questions such as “what is the length of the average man's spine” and “how tall is the average English woman”. The MCST measures set shifting and response inhibition and requires participants to sort cards on one of three possible dimensions (colour, number, shape) according to an unspoken rule. After correctly sorting six cards, the participant must shift to sort the cards along another dimension and so forth until the completion of the test. The COWA measures verbal fluency and requires participants to verbally generate as many words as possible beginning with three letters of the alphabet, being in the case of the current study F, A and S. Participants are given a 60 s time limit for each letter and must obey certain rules. The “Trail Making Test” is a test of processing speed and set shifting and requires participants to draw lines connecting a series of 25 circles. In Part A participants must connect the numbers 1–25 placed randomly over an A4 page and in Part B participants connect the letters A-L and the numbers 1–13 in alternative order. The task is scored in terms of time to complete the items. Finally, on the “Information Processing” subtests participants are required to work through a list of items. For Part A each item comprises an array of five two digit numbers and the participants’ task is to cancel out the second highest number. On Part B each item contains a four digit array, a hyphen, and then a five digit array. The participants’ task is to cross out the number in the five digit array not contained in the four digit array. Participants are given 4 min for each task. The task is scored in terms of number of items crossed out within the time limit. A test of simple motor speed, where the participant simply has to cross out the digit ‘1’ from a page of ‘1s’ is also administered.

3.1. Group difference analysis

Normality and heterogeneity were checked in the ASD and control groups using the Shapiro–Wilks test and Levene's test respectively. Depending on the results, group analysis was then conducted with either independent t -tests or Mann–Whitney tests, as appropriate. Group analysis was conducted with 77 measures derived from 17 distinct neuropsychological tests/test batteries. Where a test yields more than one sub-measure (e.g. Six Element Test yields three measures: number of tasks attempted, longest time spent on any one sub-task, and number of rule-breaks) we considered all of these sub-measures (using raw rather than scaled scores). We also considered measurements that were derived mathematically from others (e.g. Trail Making Test Part B time taken minus Part A time taken). However we did not include any measures that were sums or de facto averages of combinations of the sub-measures already considered (e.g. WAIS-III VIQ). As can be seen from Table 2 group analysis revealed limited impairment in the ASD group across the full range of tests, with only one test measure showing significant group differences at the .01 level and a further five showing significant difference at the .05 level. Observed deficits were not related to order of test administration, with the Doors and People administered at the beginning of the assessment session, the AMIPB and the Trail Making Tests administered in the middle and the Hayling towards the end of the assessment session. The remaining battery of tests revealed no significant differences between the ASD and control groups. Importantly, group analysis revealed no significant difference on the lower level tests of ability such as language comprehension, perception and short-term attention.

Mean and SD for ASD and control participants on those measures that showed a decrement according to a group-level analysis.

It is important to note that none of the significant group findings discussed above survived a Bonferroni correction at an alpha level of .05. This is not surprising in a population with marked heterogeneity of ability, consisting of both impairment and supra-normal performance. A group-level analysis would be less likely to reveal patterns of performance at the individual level that might be instructive, especially with a large battery of tests.

3.2. Single-case study analysis

For the multiple case series analysis, not only was each individual's performance compared with a normative sample, but also the relative levels of performance across tasks within the individual were considered. In order to conduct this analysis test scores for the 77 measures discussed above were converted to z -scores, based on the performance of the matched control group. The maximum range of performance on each of the 77 measures in the control group was 4.8. In the ASD group 24/77 measures (31%) showed a range exceeding this criterion set by the maximum range of the control group. As this figure is unchanged when the 6 participants who did not meet ADOS criteria are removed from the analysis we have included these participants in the remainder of the analysis in order to improve statistical power. These data quite clearly show that a defining feature of the ASD group examined here was considerable variation in performance. This variability was noted across all neuropsychological measures in our battery, including the individual WAIS-III IQ sub-measures. When summed together to produce VIQ, PIQ and FSIQ less variability was observed, although due to the underlying sub-measure variability caution needs to be applied when interpreting these summed IQ index scores. Of course, increased variance will usually be expected in a pathological group (relative to controls who are not expected to show the impairment), since an increased number will likely perform very poorly, but some will not show the characteristic under study. However the variance reported here appeared to go beyond this pattern. Some people within the ASD group were supra-normal at some tests, whilst others in the group were impaired. In other words, the increased variance for a number of measures did not derive from just impaired performance. Table 3 details those tests that showed the largest variation, and where individuals within the ASD group performed at both an impaired (<2SDs poorer than controls) and a “supra-normal” level (>2SDs above control group mean).

Neuropsychological test measures revealing variable performance in the ASD group a .

Nor was it especially the case that there were some people in the ASD group who were highly gifted across all tasks, and some individuals who were weak at all tasks. Many individuals showed evidence of both supra-normal performance on some tests, and impaired performance on others. There were no measures where only superior performance (>2SDs of controls) was detected in the ASD group. However there were some measures where only impaired performance was detected. For instance, six of the ASD group performed below the 1st percentile of the controls on the AMIPB Figure Recall test (immediate and delayed recall components), compared with only one control. This difference is significant at p = 0.046 (Fisher's Exact Test, two-tailed). None of the other measures, when submitted to such tabular analysis, reached significance individually. There are however several measures where the proportion of ASD participants who produced a noteworthy performance was greater than twice that of the control group. Thus the appropriate statistic should take the totality of this evidence into account.

To do so fully would be beyond our current knowledge of the inter-relationships and inter-dependencies between neuropsychological sub-measures. However given the size of the effects, a simplistic approach will probably suffice. Accordingly, we tallied, for each participant, the number of tasks where their performance was at least two standard deviations above or below the control mean (see Table 4 ). Comparison of the number of sub-measures that each individual performed at or below two standard deviations below the control mean showed a significant group difference, with the median of the ASD group (5.0) more than twice that of the controls (2.0; Mann–Whitney U = 134.0, p = 0.018). Furthermore, if one defines any performance either above or below two standard deviations of the control mean as unusual for each measure, the difference between the number of “unusual observations” for the ASD group and controls was highly significant (median ASD = 8.0; median controls = 3.0; U = 83.5, p = 0.0004). When the above analysis was replicated using the ASD group's performance as the normative standard no significant group differences were detected. This indicates that the present results cannot simply be a statistical artifact of comparing the performance of two groups with norms defined by the performance of just one of the groups.

Evidence of extreme range of performance in the ASD participants revealed by single-case analysis a .

Interestingly, this tendency towards atypicality of performance appeared to be a characteristic independent from one the most often-quoted neuropsychological features of an ASD group: motor speed. The biserial correlations between group membership (i.e. ASD or control) and performance on the neuropsychological measures showed that the strongest single predictor of group membership was the motor speed sub-measure of section B of the AMIPB Information Processing test ( r = −.43, p = 0.004). However, regression analysis predicting group membership showed that motor speed accounted for a separate proportion of variance in group membership from that of the total number of atypical (or unusual) performance but that total unusual performances accounted for a larger amount of variance when these variables were considered alongside each other (Motor Speed B, t = −2.86, p = .007; total unusual performance t = −3.55, p < .001). Both variables together accounted for a remarkable 34.6% of the variance (adjusted) in group membership ( F = 12.12, p < .000). Thus the prevalence of unusual or atypical performance in the ASD group cannot be attributed to some general effect of motor speed differences across the neuropsychological tests.

3.3. Relationship between cognition, ADOS and AQ

As can be seen from Table 1 , six participants did not meet ADOS criteria. We therefore removed them from the sample and re-analysed these data. There was a limited relationship between performance on the cognitive variables and the signs and symptoms of autistic spectrum disorders. Those who showed more features of the communication problems symptomatic of ASD as measured by the ADOS tended to perform more poorly on the Doors sub-measure of the Doors and People memory test (−.552, p = .009). But performance on the BORB Shape Triplets subtest actually appeared to be better in those who showed these communication signs (0.567, p = .009). Similarly, those who showed problems on the imagination sub-scale of the ADOS performed poorly on the Proverbs test (Proverbs free inquiry r = −.552, p = 0.018; multiple choice −.50, p = 0.033), and on one sub-measure of the Zoo Map test (Sequencing Two r = −.525, p = .025). However they performed somewhat better on the AMIPB Information Processing test (A adjusted: r = 0.510, p = .031). Interestingly, overall individual variability in test scores across the full battery was also strongly predictive of symptoms as measured by the ADOS. Those who showed more problems on the communication sub-scale tended to show greater variability in test scores ( r = .679, p < 0.001), and similarly those showing greater problems on the social sub-scale also tended to show greater variability in test scores ( r = .549, p = 0.010).

There was only one neuropsychological test that showed a relationship with AQ score. This was the AMIPB Story Free Recall (Immediate Recall r = −.593, delayed −.588, both p = .005). Variability in test scores was also not related to performance on the AQ.

4. Discussion

We compared participants with ASD to age and IQ matched controls on a large battery of neuropsychological tests, using both group and single-case level analysis. The group-level analysis revealed a limited set of deficits on measures of processing/motor speed, a measure of executive function tapping response initiation, inhibition and set shifting and visual memory. These deficits are consistent with findings from other recent studies with adults ( Ambery, Russell, Perry, Morris, & Murphy, 2006; Blair, Frith, Smith, Abell, & Cipolotti, 2002; Hill & Bird, 2006; Lopez, Lincoln, Ozonoff, & Lai, 2005; Minshew et al., 1992; Ozonoff et al., 2004; Williams, Goldstein, & Minshew, 2005 ). For example, Hill and Bird (2006) similarly reported deficits on the same measure of executive function tapping response initiation, inhibition and set shifting and on a measure of processing speed in their group of 22 high-functioning autism participants. However, unlike others ( Hill and Bird, 2006; Lopez et al., 2005; Ozonoff et al., 2004 ) we did not find deficits on other measures of executive function which tap elements of planning. Our finding of impaired processing/motor speed is also consistent with their finding of generally slowed psychomotor speed in this group of participants. Similarly, our finding of impairment on tests of visual memory, but not on verbal memory, is consistent with a recent finding by Ambery et al. (2006) .

No impairments were detected on the lower level tests of abilities such as short-term attention, language comprehension and perception. This supports the first hypothesis, discussed in Section 1 , in other words, that impairments in higher level abilities are not based on more primary difficulties.

In support of our second hypothesis, that patterns of deficit would vary from individual to individual within the ASD group, the analysis revealed evidence of considerable variation in abilities both between ASD participants, and also within individual participants. Both sub-normal and supra-normal performance was observed within the pattern of performance for our ASD participants. In fact, the most defining feature of the ASD group was this variability, rather than sub-normal or supra-normal performance on any one particular variable or group of variables. This pattern of marked variability was not apparent from the group-level analysis, in support of our third hypothesis. Regression analysis confirmed that this atypical performance in the ASD group could not be attributed to some general effect, such as motor speed differences across the neuropsychological tests. Finally, in keeping with our fourth hypothesis, the single-case study approach also revealed evidence of individual supra-normal performance, or strengths, that again were not apparent when the data was only analysed at the group level.

4.1. Relationships between neuropsychological tests and diagnostic symptoms

It is also worth commenting on the findings related to autism diagnosis. The ADOS and AQ measures were included to help categorise the Autism population and not as planned independent variables. As such no specific hypothesis were formulated with regard to expected findings. However, it is interesting to note that very little relationship was observed between the ADOS, the AQ and performance on the separate neuropsychological tests. Whilst failure to find significant results may in part be due to the high variability within the data, this finding does support existing studies which have failed to find a link between Autism symptoms and neuropsychological task performance (e.g. Ozonoff et al., 2004; Pellicano, Maybery, Durkin, & Maley, 2006 ). We did however find a significant relationship between the amount of individual variability on tests, and the Social and Communication sub-scales from the ADOS. This raises the possibility, which would need to be confirmed with larger group numbers, that this neuropsychological variability in itself is in part characteristic of ASD and perhaps could in future serve as an important endophenotype.

4.2. Heterogeneity as a defining feature of high-functioning ASD, and its explanations

The observation revealed by the multiple case series analysis, showed a markedly heterogeneous pattern of performance across participants, and with differing strengths and weaknesses within individuals, poses problems for single core cognitive deficit accounts of ASD. A number of other authors ( Happe et al., 2006; Willcutt et al., 2008 ) have similarly recently made the call for a shift away from single core deficit and simple linear models of pathways from underlying cause to symptom presentation. But what are the alternatives?

A possible alternative has previously been put forward by Minshew et al. (1997) . Based on their analysis of a group of 33 ASD participants Minshew et al. (1997) hypothesized that a disorder of complex information processing leads to the multiple primary deficit syndrome that is seen in ASD. Whilst Minshew et al. do report superior performance in the results of their ASD participants, the model described in the paper is still limited by the fact that it is a deficit model, albeit a multiple primary deficit model. As such, the model of Minshew et al. does not fit well with the evidence of supra-normal performance from our study. In addition, our evidence of strong performance in some ASD participants on tasks of complex information processing is also contrary to the hypothesis that a disorder of complex information processing underlies ASD.

An alternative explanation for the findings in our study is the intra-individual variability hypothesis recently explored by Geurts et al. (2008) in their study of reaction time in ADHD, ASD and Tourette's syndrome. Geurts et al. (2008) proposed that the pattern of variability observed across and within participants may be explained by frequent lapses of attention or arousal. It is possible that these lapses could also result in a pattern of variable performance across tasks in a full cognitive battery, although such an explanation seems better suited to explaining patterns of sub-normal performance than to explaining patterns of supra-normal performance or combinations of sub-normal and supra-normal performance, as observed in our study. Further, an explanation based on variability of arousal and/or attention would predict that in addition to seeing fluctuation within and across tasks in a single testing session that we should also see fluctuations across time and testing sessions. Perhaps it could be speculated that deficits may appear when arousal levels are sub-optimal and strengths when arousal levels are optimal. But evidence of good test neurocognitive stability across time in Asperger's syndrome appears to rule out such an explanation ( Nyden, Billstedt, Hjelmquist, & Gillberg, 2001 ), although the evidence in this respect is rather limited.

How else might simultaneous supra-performance in some domains and impairments in others be explained? One way might be if at critical developmental stages there is an alteration of the usual functional specialization of certain brain regions. Direct evidence for this hypothesis is now emerging. For example, at the physiological level, researchers have suggested that reduced synaptic pruning early in the life of an individual with ASD ( Frith, 2003a ) may in turn lead to an overabundance of neural pathways and encourage the formation of relatively separate populations specialized for different tasks. For example Pierce et al. (2001) reported that their ASD participants showed unique functional neural maps when processing faces, potentially as the result of aberrant developmental experience. They suggested that compared with control participants, ASD participants ‘see’ faces by utilising neural systems that are unique for each individual.

In addition, two fMRI studies by Gilbert et al. ( Gilbert, Bird, Brindley, Frith, & Burgess, 2008; Gilbert et al., 2009 ) demonstrated unusual functional specialization within medial prefrontal cortex in ASD. Gilbert et al. (2008) demonstrated a difference in the average peak co-ordinate of activation between ASD and control groups. Moreover, Gilbert et al. (2009) showed that evidence for abnormal functional organisation within medial prefrontal cortex is more readily apparent when results are analysed on a participant-by-participant basis, rather than at the group level. In their study, the authors demonstrated that fine-grained specialization within medial prefrontal cortex, at the level of individual voxels, differed between participants with ASD and an age- and IQ-matched control group. In order to obtain this type of evidence, a single-case approach was necessary. They suggested that an abnormal process by which distinct brain regions become specialized for particular functions may lead to idiosyncratic changes in the abilities of different individuals. The present study provides behavioural data directly in line with this account. Future studies would benefit from combining the case study methodology with neuroimaging data, to provide further evidence on the relationship between changes in functional brain specialization and observations of neuropsychological heterogeneity. Approaches that seek to understand this heterogeneity offer great potential to improve our understanding of the complex pattern of brain re-organisation in ASD, which may in turn improve our understanding of the underlying causes of symptom presentation ( Gilbert et al., 2009 ).

4.3. Explanations for the inconsistency of results across different studies: insights from the multiple case study approach

The limited sample sizes in this study do not allow a definitive characterization of the neuropsychological deficits in high-functioning ASD, nor even that seen within this particular set of tests. This was not the purpose of the study. But the results from the analysis at the single-case level do allow for some consideration of the plausibility of the three explanations for the inconsistency of the neuropsychological findings across different studies in the field of ASD research that were outlined in Section 1 .

The first of these possibilities was that the ASD diagnosis might encompass individuals who are highly variable in terms of their abilities and disabilities, or composed of multiple distinct subgroups, which could lead to significant population sampling differences across studies. The data here is consistent with the former proposition; confirmation of the latter would require a far larger sample. But the danger of an “averaging artifact” ( Shallice and Evans, 1978 ), where the pattern detected at a group level does not describe well any single member of the group, was highlighted well by the contrast between the striking findings at the single-case level and those much weaker ones at the group level.

The second potential explanation for the inconsistency between the findings of different studies was that the ASD diagnosis might define a group of individuals with a distinct pattern of strengths and deficits, but the deficit is such that it can cause different results according to prima facie relatively minor changes in administration or task formats. This possibility is lent support, prima facie, by the variability of performance at the single-case level. However it is challenged by the totality of the evidence: unusual performances (i.e. either supra- or sub-normal) were only seen on a limited range of the tests administered here. These ones were overwhelmingly those that had a large executive control component (including memory and perception tests with this characteristic). This seems a promising avenue for further enquiry.

The third possible explanation for inconsistency across studies is that ASD causes impairments in sensory and other processes which may then cause unpredictable impairments in tests aimed at measuring higher level tasks (e.g. problem-solving), depending on the low-level features of specific tasks (e.g. stimulus materials). This explanation was not supported at all by the present data: the ASD group were just as capable as the control group on tests of routine cognitive skills (e.g. reading, comprehension, etc.), and were matched for IQ.

4.4. Advantages of the multiple case study design for theoretical development

As Willcutt et al. (2008) note, in addition to explaining the heterogeneity across the spectrum of disorders such as ASD, it is also important that current models account for the significant neuropsychological heterogeneity at the level of the individual. The evidence from the present study challenges an explanation in terms of a single deficit or change in processing “style” underlying ASD. However the finding that the perturbations in cognition at the single-case level were almost confined to those tasks with a large executive component suggest a limit to the possibilities that might first be investigated. Further, they suggest that, at least in high-functioning ASD, one might first seek an explanation in terms of variable and abnormal development of a brain system (e.g. a multicomponential executive system), rather than a single process, or a disparate and random range of them. An investigation of that theoretical possibility is likely to require a more sophisticated approach than only reporting mean differences between groups, and it is difficult to see how this conclusion could have been reached from these data had we only done so.

Acknowledgements

This research was supported by funding from the Wellcome Trust (grant number 061171). SJG is supported by a Royal Society University Research Fellowship. We also gratefully acknowledge the support of all the participants who took part in this study. We would also like to thank Uta Frith and Sarah White for their support and assistance in conducting this research.

The Advantages and Limitations of Single Case Study Analysis

As Andrew Bennett and Colin Elman have recently noted, qualitative research methods presently enjoy “an almost unprecedented popularity and vitality… in the international relations sub-field”, such that they are now “indisputably prominent, if not pre-eminent” (2010: 499). This is, they suggest, due in no small part to the considerable advantages that case study methods in particular have to offer in studying the “complex and relatively unstructured and infrequent phenomena that lie at the heart of the subfield” (Bennett and Elman, 2007: 171). Using selected examples from within the International Relations literature[1], this paper aims to provide a brief overview of the main principles and distinctive advantages and limitations of single case study analysis. Divided into three inter-related sections, the paper therefore begins by first identifying the underlying principles that serve to constitute the case study as a particular research strategy, noting the somewhat contested nature of the approach in ontological, epistemological, and methodological terms. The second part then looks to the principal single case study types and their associated advantages, including those from within the recent ‘third generation’ of qualitative International Relations (IR) research. The final section of the paper then discusses the most commonly articulated limitations of single case studies; while accepting their susceptibility to criticism, it is however suggested that such weaknesses are somewhat exaggerated. The paper concludes that single case study analysis has a great deal to offer as a means of both understanding and explaining contemporary international relations.

The term ‘case study’, John Gerring has suggested, is “a definitional morass… Evidently, researchers have many different things in mind when they talk about case study research” (2006a: 17). It is possible, however, to distil some of the more commonly-agreed principles. One of the most prominent advocates of case study research, Robert Yin (2009: 14) defines it as “an empirical enquiry that investigates a contemporary phenomenon in depth and within its real-life context, especially when the boundaries between phenomenon and context are not clearly evident”. What this definition usefully captures is that case studies are intended – unlike more superficial and generalising methods – to provide a level of detail and understanding, similar to the ethnographer Clifford Geertz’s (1973) notion of ‘thick description’, that allows for the thorough analysis of the complex and particularistic nature of distinct phenomena. Another frequently cited proponent of the approach, Robert Stake, notes that as a form of research the case study “is defined by interest in an individual case, not by the methods of inquiry used”, and that “the object of study is a specific, unique, bounded system” (2008: 443, 445). As such, three key points can be derived from this – respectively concerning issues of ontology, epistemology, and methodology – that are central to the principles of single case study research.

First, the vital notion of ‘boundedness’ when it comes to the particular unit of analysis means that defining principles should incorporate both the synchronic (spatial) and diachronic (temporal) elements of any so-called ‘case’. As Gerring puts it, a case study should be “an intensive study of a single unit… a spatially bounded phenomenon – e.g. a nation-state, revolution, political party, election, or person – observed at a single point in time or over some delimited period of time” (2004: 342). It is important to note, however, that – whereas Gerring refers to a single unit of analysis – it may be that attention also necessarily be given to particular sub-units. This points to the important difference between what Yin refers to as an ‘holistic’ case design, with a single unit of analysis, and an ’embedded’ case design with multiple units of analysis (Yin, 2009: 50-52). The former, for example, would examine only the overall nature of an international organization, whereas the latter would also look to specific departments, programmes, or policies etc.

Secondly, as Tim May notes of the case study approach, “even the most fervent advocates acknowledge that the term has entered into understandings with little specification or discussion of purpose and process” (2011: 220). One of the principal reasons for this, he argues, is the relationship between the use of case studies in social research and the differing epistemological traditions – positivist, interpretivist, and others – within which it has been utilised. Philosophy of science concerns are obviously a complex issue, and beyond the scope of much of this paper. That said, the issue of how it is that we know what we know – of whether or not a single independent reality exists of which we as researchers can seek to provide explanation – does lead us to an important distinction to be made between so-called idiographic and nomothetic case studies (Gerring, 2006b). The former refers to those which purport to explain only a single case, are concerned with particularisation, and hence are typically (although not exclusively) associated with more interpretivist approaches. The latter are those focused studies that reflect upon a larger population and are more concerned with generalisation, as is often so with more positivist approaches[2]. The importance of this distinction, and its relation to the advantages and limitations of single case study analysis, is returned to below.

Thirdly, in methodological terms, given that the case study has often been seen as more of an interpretivist and idiographic tool, it has also been associated with a distinctly qualitative approach (Bryman, 2009: 67-68). However, as Yin notes, case studies can – like all forms of social science research – be exploratory, descriptive, and/or explanatory in nature. It is “a common misconception”, he notes, “that the various research methods should be arrayed hierarchically… many social scientists still deeply believe that case studies are only appropriate for the exploratory phase of an investigation” (Yin, 2009: 6). If case studies can reliably perform any or all three of these roles – and given that their in-depth approach may also require multiple sources of data and the within-case triangulation of methods – then it becomes readily apparent that they should not be limited to only one research paradigm. Exploratory and descriptive studies usually tend toward the qualitative and inductive, whereas explanatory studies are more often quantitative and deductive (David and Sutton, 2011: 165-166). As such, the association of case study analysis with a qualitative approach is a “methodological affinity, not a definitional requirement” (Gerring, 2006a: 36). It is perhaps better to think of case studies as transparadigmatic; it is mistaken to assume single case study analysis to adhere exclusively to a qualitative methodology (or an interpretivist epistemology) even if it – or rather, practitioners of it – may be so inclined. By extension, this also implies that single case study analysis therefore remains an option for a multitude of IR theories and issue areas; it is how this can be put to researchers’ advantage that is the subject of the next section.

Having elucidated the defining principles of the single case study approach, the paper now turns to an overview of its main benefits. As noted above, a lack of consensus still exists within the wider social science literature on the principles and purposes – and by extension the advantages and limitations – of case study research. Given that this paper is directed towards the particular sub-field of International Relations, it suggests Bennett and Elman’s (2010) more discipline-specific understanding of contemporary case study methods as an analytical framework. It begins however, by discussing Harry Eckstein’s seminal (1975) contribution to the potential advantages of the case study approach within the wider social sciences.

Eckstein proposed a taxonomy which usefully identified what he considered to be the five most relevant types of case study. Firstly were so-called configurative-idiographic studies, distinctly interpretivist in orientation and predicated on the assumption that “one cannot attain prediction and control in the natural science sense, but only understanding ( verstehen )… subjective values and modes of cognition are crucial” (1975: 132). Eckstein’s own sceptical view was that any interpreter ‘simply’ considers a body of observations that are not self-explanatory and “without hard rules of interpretation, may discern in them any number of patterns that are more or less equally plausible” (1975: 134). Those of a more post-modernist bent, of course – sharing an “incredulity towards meta-narratives”, in Lyotard’s (1994: xxiv) evocative phrase – would instead suggest that this more free-form approach actually be advantageous in delving into the subtleties and particularities of individual cases.

Eckstein’s four other types of case study, meanwhile, promote a more nomothetic (and positivist) usage. As described, disciplined-configurative studies were essentially about the use of pre-existing general theories, with a case acting “passively, in the main, as a receptacle for putting theories to work” (Eckstein, 1975: 136). As opposed to the opportunity this presented primarily for theory application, Eckstein identified heuristic case studies as explicit theoretical stimulants – thus having instead the intended advantage of theory-building. So-called p lausibility probes entailed preliminary attempts to determine whether initial hypotheses should be considered sound enough to warrant more rigorous and extensive testing. Finally, and perhaps most notably, Eckstein then outlined the idea of crucial case studies , within which he also included the idea of ‘most-likely’ and ‘least-likely’ cases; the essential characteristic of crucial cases being their specific theory-testing function.

Whilst Eckstein’s was an early contribution to refining the case study approach, Yin’s (2009: 47-52) more recent delineation of possible single case designs similarly assigns them roles in the applying, testing, or building of theory, as well as in the study of unique cases[3]. As a subset of the latter, however, Jack Levy (2008) notes that the advantages of idiographic cases are actually twofold. Firstly, as inductive/descriptive cases – akin to Eckstein’s configurative-idiographic cases – whereby they are highly descriptive, lacking in an explicit theoretical framework and therefore taking the form of “total history”. Secondly, they can operate as theory-guided case studies, but ones that seek only to explain or interpret a single historical episode rather than generalise beyond the case. Not only does this therefore incorporate ‘single-outcome’ studies concerned with establishing causal inference (Gerring, 2006b), it also provides room for the more postmodern approaches within IR theory, such as discourse analysis, that may have developed a distinct methodology but do not seek traditional social scientific forms of explanation.

Applying specifically to the state of the field in contemporary IR, Bennett and Elman identify a ‘third generation’ of mainstream qualitative scholars – rooted in a pragmatic scientific realist epistemology and advocating a pluralistic approach to methodology – that have, over the last fifteen years, “revised or added to essentially every aspect of traditional case study research methods” (2010: 502). They identify ‘process tracing’ as having emerged from this as a central method of within-case analysis. As Bennett and Checkel observe, this carries the advantage of offering a methodologically rigorous “analysis of evidence on processes, sequences, and conjunctures of events within a case, for the purposes of either developing or testing hypotheses about causal mechanisms that might causally explain the case” (2012: 10).

Harnessing various methods, process tracing may entail the inductive use of evidence from within a case to develop explanatory hypotheses, and deductive examination of the observable implications of hypothesised causal mechanisms to test their explanatory capability[4]. It involves providing not only a coherent explanation of the key sequential steps in a hypothesised process, but also sensitivity to alternative explanations as well as potential biases in the available evidence (Bennett and Elman 2010: 503-504). John Owen (1994), for example, demonstrates the advantages of process tracing in analysing whether the causal factors underpinning democratic peace theory are – as liberalism suggests – not epiphenomenal, but variously normative, institutional, or some given combination of the two or other unexplained mechanism inherent to liberal states. Within-case process tracing has also been identified as advantageous in addressing the complexity of path-dependent explanations and critical junctures – as for example with the development of political regime types – and their constituent elements of causal possibility, contingency, closure, and constraint (Bennett and Elman, 2006b).

Bennett and Elman (2010: 505-506) also identify the advantages of single case studies that are implicitly comparative: deviant, most-likely, least-likely, and crucial cases. Of these, so-called deviant cases are those whose outcome does not fit with prior theoretical expectations or wider empirical patterns – again, the use of inductive process tracing has the advantage of potentially generating new hypotheses from these, either particular to that individual case or potentially generalisable to a broader population. A classic example here is that of post-independence India as an outlier to the standard modernisation theory of democratisation, which holds that higher levels of socio-economic development are typically required for the transition to, and consolidation of, democratic rule (Lipset, 1959; Diamond, 1992). Absent these factors, MacMillan’s single case study analysis (2008) suggests the particularistic importance of the British colonial heritage, the ideology and leadership of the Indian National Congress, and the size and heterogeneity of the federal state.

Most-likely cases, as per Eckstein above, are those in which a theory is to be considered likely to provide a good explanation if it is to have any application at all, whereas least-likely cases are ‘tough test’ ones in which the posited theory is unlikely to provide good explanation (Bennett and Elman, 2010: 505). Levy (2008) neatly refers to the inferential logic of the least-likely case as the ‘Sinatra inference’ – if a theory can make it here, it can make it anywhere. Conversely, if a theory cannot pass a most-likely case, it is seriously impugned. Single case analysis can therefore be valuable for the testing of theoretical propositions, provided that predictions are relatively precise and measurement error is low (Levy, 2008: 12-13). As Gerring rightly observes of this potential for falsification:

“a positivist orientation toward the work of social science militates toward a greater appreciation of the case study format, not a denigration of that format, as is usually supposed” (Gerring, 2007: 247, emphasis added).

In summary, the various forms of single case study analysis can – through the application of multiple qualitative and/or quantitative research methods – provide a nuanced, empirically-rich, holistic account of specific phenomena. This may be particularly appropriate for those phenomena that are simply less amenable to more superficial measures and tests (or indeed any substantive form of quantification) as well as those for which our reasons for understanding and/or explaining them are irreducibly subjective – as, for example, with many of the normative and ethical issues associated with the practice of international relations. From various epistemological and analytical standpoints, single case study analysis can incorporate both idiographic sui generis cases and, where the potential for generalisation may exist, nomothetic case studies suitable for the testing and building of causal hypotheses. Finally, it should not be ignored that a signal advantage of the case study – with particular relevance to international relations – also exists at a more practical rather than theoretical level. This is, as Eckstein noted, “that it is economical for all resources: money, manpower, time, effort… especially important, of course, if studies are inherently costly, as they are if units are complex collective individuals ” (1975: 149-150, emphasis added).

Limitations

Single case study analysis has, however, been subject to a number of criticisms, the most common of which concern the inter-related issues of methodological rigour, researcher subjectivity, and external validity. With regard to the first point, the prototypical view here is that of Zeev Maoz (2002: 164-165), who suggests that “the use of the case study absolves the author from any kind of methodological considerations. Case studies have become in many cases a synonym for freeform research where anything goes”. The absence of systematic procedures for case study research is something that Yin (2009: 14-15) sees as traditionally the greatest concern due to a relative absence of methodological guidelines. As the previous section suggests, this critique seems somewhat unfair; many contemporary case study practitioners – and representing various strands of IR theory – have increasingly sought to clarify and develop their methodological techniques and epistemological grounding (Bennett and Elman, 2010: 499-500).

A second issue, again also incorporating issues of construct validity, concerns that of the reliability and replicability of various forms of single case study analysis. This is usually tied to a broader critique of qualitative research methods as a whole. However, whereas the latter obviously tend toward an explicitly-acknowledged interpretive basis for meanings, reasons, and understandings:

“quantitative measures appear objective, but only so long as we don’t ask questions about where and how the data were produced… pure objectivity is not a meaningful concept if the goal is to measure intangibles [as] these concepts only exist because we can interpret them” (Berg and Lune, 2010: 340).

The question of researcher subjectivity is a valid one, and it may be intended only as a methodological critique of what are obviously less formalised and researcher-independent methods (Verschuren, 2003). Owen (1994) and Layne’s (1994) contradictory process tracing results of interdemocratic war-avoidance during the Anglo-American crisis of 1861 to 1863 – from liberal and realist standpoints respectively – are a useful example. However, it does also rest on certain assumptions that can raise deeper and potentially irreconcilable ontological and epistemological issues. There are, regardless, plenty such as Bent Flyvbjerg (2006: 237) who suggest that the case study contains no greater bias toward verification than other methods of inquiry, and that “on the contrary, experience indicates that the case study contains a greater bias toward falsification of preconceived notions than toward verification”.

The third and arguably most prominent critique of single case study analysis is the issue of external validity or generalisability. How is it that one case can reliably offer anything beyond the particular? “We always do better (or, in the extreme, no worse) with more observation as the basis of our generalization”, as King et al write; “in all social science research and all prediction, it is important that we be as explicit as possible about the degree of uncertainty that accompanies out prediction” (1994: 212). This is an unavoidably valid criticism. It may be that theories which pass a single crucial case study test, for example, require rare antecedent conditions and therefore actually have little explanatory range. These conditions may emerge more clearly, as Van Evera (1997: 51-54) notes, from large-N studies in which cases that lack them present themselves as outliers exhibiting a theory’s cause but without its predicted outcome. As with the case of Indian democratisation above, it would logically be preferable to conduct large-N analysis beforehand to identify that state’s non-representative nature in relation to the broader population.

There are, however, three important qualifiers to the argument about generalisation that deserve particular mention here. The first is that with regard to an idiographic single-outcome case study, as Eckstein notes, the criticism is “mitigated by the fact that its capability to do so [is] never claimed by its exponents; in fact it is often explicitly repudiated” (1975: 134). Criticism of generalisability is of little relevance when the intention is one of particularisation. A second qualifier relates to the difference between statistical and analytical generalisation; single case studies are clearly less appropriate for the former but arguably retain significant utility for the latter – the difference also between explanatory and exploratory, or theory-testing and theory-building, as discussed above. As Gerring puts it, “theory confirmation/disconfirmation is not the case study’s strong suit” (2004: 350). A third qualification relates to the issue of case selection. As Seawright and Gerring (2008) note, the generalisability of case studies can be increased by the strategic selection of cases. Representative or random samples may not be the most appropriate, given that they may not provide the richest insight (or indeed, that a random and unknown deviant case may appear). Instead, and properly used , atypical or extreme cases “often reveal more information because they activate more actors… and more basic mechanisms in the situation studied” (Flyvbjerg, 2006). Of course, this also points to the very serious limitation, as hinted at with the case of India above, that poor case selection may alternatively lead to overgeneralisation and/or grievous misunderstandings of the relationship between variables or processes (Bennett and Elman, 2006a: 460-463).

As Tim May (2011: 226) notes, “the goal for many proponents of case studies […] is to overcome dichotomies between generalizing and particularizing, quantitative and qualitative, deductive and inductive techniques”. Research aims should drive methodological choices, rather than narrow and dogmatic preconceived approaches. As demonstrated above, there are various advantages to both idiographic and nomothetic single case study analyses – notably the empirically-rich, context-specific, holistic accounts that they have to offer, and their contribution to theory-building and, to a lesser extent, that of theory-testing. Furthermore, while they do possess clear limitations, any research method involves necessary trade-offs; the inherent weaknesses of any one method, however, can potentially be offset by situating them within a broader, pluralistic mixed-method research strategy. Whether or not single case studies are used in this fashion, they clearly have a great deal to offer.

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[1] The paper follows convention by differentiating between ‘International Relations’ as the academic discipline and ‘international relations’ as the subject of study.

[2] There is some similarity here with Stake’s (2008: 445-447) notion of intrinsic cases, those undertaken for a better understanding of the particular case, and instrumental ones that provide insight for the purposes of a wider external interest.

[3] These may be unique in the idiographic sense, or in nomothetic terms as an exception to the generalising suppositions of either probabilistic or deterministic theories (as per deviant cases, below).

[4] Although there are “philosophical hurdles to mount”, according to Bennett and Checkel, there exists no a priori reason as to why process tracing (as typically grounded in scientific realism) is fundamentally incompatible with various strands of positivism or interpretivism (2012: 18-19). By extension, it can therefore be incorporated by a range of contemporary mainstream IR theories.

— Written by: Ben Willis Written at: University of Plymouth Written for: David Brockington Date written: January 2013

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Contributions of human cultures to biodiversity and ecosystem conservation

Carolina Levis ORCID: orcid.org/0000-0002-8425-9479 1 , 2 ,
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The expansion of globalized industrial societies is causing global warming, ecosystem degradation, and species and language extinctions worldwide. Mainstream conservation efforts still focus on nature protection strategies to revert this crisis, often overlooking the essential roles of Indigenous Peoples and Local Communities (IP&LC) in protecting biodiversity and ecosystems globally. Here we assess the scientific literature to identify relationships between biodiversity (including ecosystem diversity) and cultural diversity, and investigate how these connections may affect conservation outcomes in tropical lowland South America. Our assessment reveals a network of interactions and feedbacks between biodiversity and diverse IP&LC, suggesting interconnectedness and interdependencies from which multiple benefits to nature and societies emerge. We illustrate our findings with five case studies of successful conservation models, described as consolidated or promising ‘social–ecological hope spots’, that show how engagement with IP&LC of various cultures may be the best hope for biodiversity and ecosystem conservation, particularly when aligned with science and technology. In light of these five inspiring cases, we argue that conservation science and policies need to recognize that protecting and promoting both biological and cultural diversities can provide additional co-benefits and solutions to maintain ecosystems resilient in the face of global changes.

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Koch, A., Brierley, C., Maslin, M. M. & Lewis, S. L. Earth system impacts of the European arrival and Great Dying in the Americas after 1492. Quat. Sci. Rev. 207 , 13–36 (2019).

Flores, B. M. & Staal, A. Feedback in tropical forests of the Anthropocene. Glob. Change Biol. 28 , 5041–5061 (2022).

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Acknowledgements

C.L. thanks the Brazilian Federal Agency for Suport and Evaluation of Graduate Education (CAPES, 88887.474572/2020-00), Brazilian National Council for Scientific and Technological Development (CNPq, 159440/2018-1 and 151231/2021-4) for post-doctoral fellowships, CAPES for the CAPES Thesis Award 2019, and Brazil LAB (Luso-Afro-Brazilian Studies) at the Princeton Institute for International and Regional Studies of Princeton University for supporting her research. B.M.F. is supported by the Instituto Serrapilheira (Serra‐1709‐18983). C.R.C. thanks CNPq (303477/2018-0) for a research fellowship, N.P. thanks CNPq (310443/2015-6) for a research fellowship. M.C.G.P. thanks CAPES via the Amazon Face Program (INPA/CAPES 88881.154644/2017-01 and 88887.373727/2019-00). Materials pertaining to the Xingu hope spot were supported by NSF (BCS 0004487, 053129, 1660459), the William Talbott Hillman Foundation, the Pennywise Foundation and the Puente Institute.

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Carolina Levis

Instituto Juruá, Manaus, Brazil

João Vitor Campos-Silva

Instituto de Ciências Biológicas e da Saúde, Universidade Federal de Alagoas, Maceió, Brazil

João Vitor Campos-Silva & Charles R. Clement

Instituto Nacional de Pesquisas da Amazônia, Manaus, Brazil

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C.L., B.M.F. and C.R.C. conceived the study. C.L., B.M.F., C.R.C. and N.P. conducted the literature review. J.V.C.-S. and C.L. were responsible for all promising case studies and M.H., W.D., H.L., C.F., B.F., J.W., B.M., M.S., T.W.K., H.K., K.W., K.K. and A.K. were responsible for the Xingu hope spot. C.L., B.M.F., C.R.C., N.P., J.V.C.-S., A.S., M.C.G.P., M.H., W.D., H.L., C.F., B.F., J.W., B.M., M.S., T.W.K., H.K., K.W., K.K. and A.K. interpreted the full literature review. C.L. led the writing of the article, and B.M.F., C.R.C., N.P., J.V.C.-S., A.S., M.C.G.P., M.H., H.L., J.W. and C.F. substantially revised it. All authors agreed to this version for submission.

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Extended data

Extended data fig. 1 xingu hope spot in the southern transitional forest of brazilian amazonia..

( a ) ArcGIS maps including the TIX and surroundings, archaeological sites and features and modern villages. ( b ) Pre-Columbian complex systems of land management and urbanized landscapes in the TIX. ( c ) Kuikuru modern village. ( d ) Indigenous participation in mapping and real-time data collection. Image credits: AIKAX 123 .

Extended Data Fig. 2 Collaborative management of giant arapaima fish in Amazonian floodplains.

( a ) Co-management of arapaima habitats. ( b ) Harvesting arapaima fishes according to local needs. ( c ) Improving welfare and gender equality. Photos credits: Marcos Amend/Instituto Juruá and Andre Dib/Insituto Juruá.

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Levis, C., Flores, B.M., Campos-Silva, J.V. et al. Contributions of human cultures to biodiversity and ecosystem conservation. Nat Ecol Evol (2024). https://doi.org/10.1038/s41559-024-02356-1

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DOI : https://doi.org/10.1038/s41559-024-02356-1

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Raph Goldacre 1 ,
http://orcid.org/0000-0002-4848-6156 Michael Trubshaw 2 ,
Eva J A Morris 1 ,
http://orcid.org/0000-0001-5490-1697 Kevin Talbot 2 ,
Michael J Goldacre 1 ,
http://orcid.org/0000-0003-1063-3277 Alexander Guy Thompson 2 ,
http://orcid.org/0000-0003-0267-3180 Martin R Turner 2
1 Big Data Institute, Nuffield Department of Population Health , University of Oxford , Oxford , UK
2 Nuffield Department of Clinical Neurosciences , University of Oxford , Oxford , UK
Correspondence to Prof Martin R Turner, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, OX1 2JD, UK; martin.turner{at}ndcn.ox.ac.uk

Background Venous thromboembolism (VTE) can occur in amyotrophic lateral sclerosis (ALS) and pulmonary embolism causes death in a minority of cases. The benefits of preventing VTE must be weighed against the risks. An accurate estimate of the incidence of VTE in ALS is crucial to assessing this balance.

Methods This retrospective record-linkage cohort study derived data from the Hospital Episode Statistics database, covering admissions to England’s hospitals from 1 April 2003 to 31 December 2019 and included 21 163 patients with ALS and 17 425 337 controls. Follow-up began at index admission and ended at VTE admission, death or 2 years (whichever came sooner). Adjusted HRs (aHRs) for VTE were calculated, controlling for confounders.

Results The incidence of VTE in the ALS cohort was 18.8/1000 person-years. The relative risk of VTE in ALS was significantly greater than in controls (aHR 2.7, 95% CI 2.4 to 3.0). The relative risk of VTE in patients with ALS under 65 years was five times higher than controls (aHR 5.34, 95% CI 4.6 to 6.2), and higher than that of patients over 65 years compared with controls (aHR 1.86, 95% CI 1.62 to 2.12).

Conclusions Patients with ALS are at a higher risk of developing VTE, but this is similar in magnitude to that reported in other chronic neurological conditions associated with immobility, such as multiple sclerosis, which do not routinely receive VTE prophylaxis. Those with ALS below the median age of symptom onset have a notably higher relative risk. A reappraisal of the case for routine antithrombotic therapy in those diagnosed with ALS now requires a randomised controlled trial.

MOTOR NEURON DISEASE
EPIDEMIOLOGY

Data availability statement

Data may be obtained from a third party and are not publicly available. The linked national HES-APC and mortality data used in this study were obtained from NHS Digital and may be available upon application to NHS Digital.

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/ .

https://doi.org/10.1136/jnnp-2024-333399

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WHAT IS ALREADY KNOWN ON THIS TOPIC

Venous thromboembolism (VTE) occurs more frequently in chronic neurological disorders associated with physical disability, including those with amyotrophic lateral sclerosis (ALS).

VTE is the direct cause of death in a minority of those with ALS.

Routine VTE prophylaxis is not currently recommended in ALS, but the balance of benefit versus risk depends on accurate estimates of incidence in population-based studies.

WHAT THIS STUDY ADDS

A large UK hospital record-linkage study of more than 20 000 patients with ALS demonstrated an increased risk of VTE in patients with ALS (adjusted HR (aHR) 2.7, 95% CI 2.4 to 3.0).

Patients aged under 65 had the highest relative risk (aHR 5.34, 95% CI 4.6 to 6.2).

HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY

The risk of VTE in ALS is significantly raised and preventable.

The case for routine VTE prophylaxis in those diagnosed with ALS is nuanced and a randomised controlled trial needs consideration.

Introduction

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterised by progressive muscle weakness due to the loss of motor neurons. Median survival from symptom onset is 30 months. Although the most common cause of death in ALS is respiratory muscle compromise with associated bronchopneumonia, venous thromboembolism (VTE) is recognised as a cause of sudden unexpected death. 1

VTE comprises deep vein thrombosis (DVT) and pulmonary embolism (PE), and respectively describes the process of pathological clotting of the blood within the deep leg veins and embolisation to the pulmonary arteries. Risk factors for VTE include any disease process or environmental influence which increases blood stasis, hypercoagulability or endothelial injury (commonly known as Virchow’s triad). 2 The increased risk of VTE in ALS is thought to primarily relate to reduced mobility, which exacerbates venous pooling in the lower limbs. 3 Large PEs may lead to a failure of venous return to the left heart and blood oxygenation causing cardiovascular collapse. The 30-day mortality estimates from a single DVT and PE event are 3% and 31%, respectively. 4

PEs can also present silently—so-called ‘incidental PEs’. A meta-analysis estimated the prevalence of incidental PEs, identified through CT scans across a range of comorbidities, at 2.6% (95% CI 1.9% to 2.1%). 5 Estimates for progression of silent PEs to fatal disease range from 0% to 25%. 6–8 Although conclusions from the literature are ambiguous, current consensus guidelines advise that incidental PE should be managed identically to symptomatic PE. 8 There are no studies investigating the prevalence of incidental PEs in ALS although recent work found a 2% incidence of incidental DVT in a cohort of admitted patients with ALS in Japan. 9

Preventing VTE is possible through mechanical (stocking or intermittent pneumatic compression) or pharmacological prophylaxis. The latter options include low molecular weight heparin (LMWH), unfractionated heparin, direct oral anticoagulants (DOACs) and aspirin. 10–13 In all cases, the risks of both occurrence and significant complications of VTE must be weighed with the risks of the prophylaxis. For pharmacological prophylaxis, this is the increased risk of bleeding events, and for mechanical prophylaxis this is the risk of skin damage through compression-related tissue ischaemia. 11

Of the few studies of VTE in ALS specifically, the majority have been observational, small and clinic based. They have estimated yearly incidence of VTE in ALS between 2.7% and 11.2%. 1 3 14–20 This compares to an overall population rate estimate of 0.1%, which rises to 0.5% in those older than 80. 21 22 The only large population-based study reported a yearly VTE incidence of 2% in a cohort of 4205 patients with ALS for a US health insurance claims database. 23

Through access to a large observational, retrospective cohort of hospital record-linkage data from the National Health Service (NHS) in England, we aimed to characterise both the incidence of VTE in ALS and the relative risk of VTE in ALS compared with a reference cohort of hospital controls.

Data sources and study population

A data extract was derived from the English National Hospital Episode Statistics Admitted Patient Care (HES-APC) database with linkage to national mortality civil registrations under data access agreement reference DARS-NIC-315419-F3W7K. The database is estimated to contain 98%–99% of hospital activity in England (around 20 million episodes per year). 24 The data extract used in this study comprised all HES-APC and mortality records belonging to three categories of patients: (1) those admitted to NHS hospitals between 1 April 2003 and 31 December 2019 with a record of ALS (ICD10 G12.2) coded as the primary diagnosis, hereafter termed the ‘ALS cohort’; (2) those admitted during the same time period with one of the diagnoses or procedures listed as the primary cause of admission, hereafter termed the reference cohort* and (3) those who had a VTE (ICD10 I26, I80–I82) coded in any diagnostic position on a HES-APC record or, if relevant, their death record during the same time period, irrespective of whether they were also included in (1) or (2).

*The reference cohort comprised 17 425 337 individuals admitted to hospital for vasectomy, cataract treatment, single delivery, upper respiratory tract infections, inguinal hernia, gallstones, nasal polyps, deflected septum, bunions, limb fractures, dislocations/sprains/strains, teeth disorders, otitis, haemorrhoids, nail disorders, sebaceous cyst, knee internal derangement, bruising, appendectomy, dilation and currettage, tonsillectomy, hip replacement, knee replacement, tendency to fall, urinary tract infection. The reference cohort was designed to be as representative as possible of the general population in terms of general health status by selecting a diverse range of conditions that are common and relatively minor. Herbert et al provide further information and discussion on the design and utility of the HES-APC. 24

Study design

The study design was a retrospective cohort study. Each patient’s cohort entry date was the discharge date of their index admission, which for the ALS cohort was the patient’s earliest known admission for ALS coded as the primary diagnosis, and for the reference cohort was the patient’s earliest known admission for one of the reference conditions . The patients in each cohort were then ‘followed up’ through record linkage for any subsequent admission up to 2 years later where VTE was coded in any diagnostic position. The null hypothesis was that the incidence of VTE would be the same in both cohorts.

Statistical analysis

Patients in each cohort were followed for up to 2 years from the date of cohort entry until the date of first known VTE diagnosis, death or the end of the follow‐up period (31 December 2019), whichever came first. Age-sex-specific annual incidence rates of VTE hospitalisation in each cohort were calculated per 1000 person-years (censoring for death). Multivariable Cox proportional hazards regression models were used to estimate the adjusted HRs (aHR) of VTE in the ALS cohort compared with the reference cohort, with adjustment for age (in 5‐year groups), sex, year of index admission, region of residence (nine NHS regions), patients’ Index of Multiple Deprivation score in quintiles, ethnic category, and Charlson Comorbidity Score. It was not possible to include smoking and body mass index as they are not routinely recorded in the HES-APC. Individual-level prescribing data was not available. Time from cohort entry was used as the underlying time variable.

To examine the representativeness of the reference cohort compared with the general population in relation to VTE risk, we compared the age-sex-specific rates of annual incidence of VTE hospitalisation in the reference cohort with the ‘true’ annual incidence of VTE hospitalisation in the English population. The latter was calculated by ascertaining the age-sex specific counts of VTE hospitalisation in each calendar year of national HES and dividing these by the corresponding English national age-sex-specific mid-year population denominators in each calendar year (obtained from the national Office for National Statistics), and then multiplying by 1000. These rates were then compared with the age-sex-specific rates of VTE in the reference cohort as calculated in the longitudinal analysis. To explore the possibility that recent discharge from hospital might itself be associated with an elevated risk of VTE in early follow-up, follow-up in the reference cohort was divided into four 6-month periods (0–6 months, 6–12 months, 12–18 months and 18–24 months), and the incidence of VTE per 1000 person-years in each period separately was then compared with the true incidence of VTE in the general population. The actual general population was not used as the reference population because the national population denominators were aggregated by age and sex only, whereas the cohort of hospital controls enabled greater internal validity, multivariable adjustment and flexibility in the analysis of follow-up time.

The ALS and reference cohorts comprised, respectively, 21 163 and 17 425 337 individuals. Figure 1 summarises the age–sex distribution of the ALS cohort. The mean age of patients in the ALS cohort was 68 years (SD 12.2).

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Age–sex distribution of patients included in the ALS cohort. ALS, amyotrophic lateral sclerosis.

Figure 2 compares the age-sex-specific incidence of VTE in the reference cohort (by time since index admission) with that of the general population: in the first 6 months of follow-up, incidence of VTE in the reference cohort was substantially higher than in the general population; thereafter, incidence of VTE in the reference cohort closely resembled that of the true general population. Thus, the reference cohort after the first 6 months of follow-up could be regarded as validly equivalent to the ‘general population’ in terms of background risk of VTE, with the first 6 months of follow-up representing a short-term additional risk conferred by recent hospitalisation.

Annual incidence of hospital recorded VTE in England: reference cohort (by time since index admission) versus general population. VTE, venous thromboembolism.

The overall incidence of VTE in the ALS cohort was 18.8 per 1000 person-years. After multivariable adjustment, the overall incidence of VTE in the ALS cohort was nearly three times higher than in the reference cohort (aHR 2.7, 95% CI 2.4 to 3.0) . There was a significantly increased risk of both PE (315 cases observed; aHR 3.4, 95% CI 3.0 to 3.9) and DVT (232 cases observed; aHR 2.2, 95% CI 1.9 to 2.5). Figure 3 shows the absolute incidence rates of VTE in the ALS cohort (unadjusted) and aHRs, stratified by sex, age group (<65 and 65+ years) and follow-up period (0–6 months, 6–24 months). While the absolute incidence of VTE in the ALS cohort was similar in older patients (aged 65+) and younger patients (aged <65), the aHR was significantly higher in younger patients than older patients (likelihood ratio test for heterogeneity χ 2 (1)=104.6; p<0.0001). The aHR was significantly higher in months 6–24 of follow-up than in the first 6 months (likelihood ratio test for heterogeneity χ 2 (1)=11.5; p=0.0007).

Forest plot showing adjusted HR for VTE in ALS by patient group. aHR, adjusted HR; ALS, amyotrophic lateral sclerosis; IR, incidence rate; VTE, venous thromboembolism.

This large population-based study showed that the risk of VTE in the ALS cohort of patients was nearly three times higher than the reference cohort after multivariable adjustment. The higher aHR in younger patients with ALS, and in later periods of follow-up, suggest that ALS directly influences risk of VTE, independently of biological ageing and recent hospitalisation. This might relate to the slower rate of disease progression and tendency to limb predominance in younger patients with the consequence of prolonged immobility. 25 An alternative explanation might be that the background prevalence of immobility (and therefore VTE risk) is so low in the younger general population, that ALS (and therefore immobility) disproportionately increases VTE risk in such age groups. Another large record-linkage study reported a similar risk to our overall estimate (HR 3.3, 95% CI 2.6 to 4.0) and a similar yearly incidence of 2%. 26 Multiple previous smaller studies comparably found an increased incidence of VTE in ALS. 1 3 14–18 Some of these studies have identified significant phenotype risk differences. Most notably, lower-limb-dominated patients with ALS showed an annual VTE incidence as high as 35%. 3 16 A summary of published literature is in table 1 . This study also found that in patients with ALS the relative risk of PE was higher than that of DVT (aHR 3.4 vs 2.2). One reason for this might be that DVT is more susceptible than PE to underdetection and lower hospital presentation rates in patients with ALS, in which case the relative risk of DVT could be underestimated.

View inline

Summary of VTE in ALS literature

It is likely that primary VTE prophylaxis in ALS is currently avoided due to ambiguity over the precise balance of risks associated with such therapy, rather than the existence of conclusive evidence proving its disproportionate excess harm. There is a distinct lack of high-quality randomised control trials assessing this balance of risks in neurological diseases. It is unlikely that the ALS disease process itself increases coagulability, but rather the associated immobility. Immobile individuals who receive regular VTE prophylaxis include those acutely poststroke (21-day VTE risk of 40%) and spinal cord injury (36 month VTE risk of 23.4%). 27 28 However, conditions with comparable VTE risk to ALS such as multiple sclerosis (aHR 2.56 (95% CI 2.06 to 3.20) and cancer (aHR 4.7 (95% CI 4.5 to 4.9), do not routinely receive routine VTE prophylaxis. 29–31 An exception is patients with multiple myeloma on prothrombotic chemotherapy such as lenalidomide, whose yearly risk of VTE without prophylaxis is 12% and is reduced to 2.3% with low-dose aspirin therapy. 32 Aspirin is also effective as prophylaxis in postsurgical patients. 33 If pharmacological prophylaxis were adopted in ALS, aspirin may represent a safer drug candidate due to its minimal effect on the risk of serious bleeding events such as cerebral or gastrointestinal haemorrhage (RR 1.4 95% CI 1.2 to 1.7). 34 Graduated compression stockings represent a mechanical alternative, however high-quality evidence proving their efficacy is limited only to hospitalised surgical patients and their long-term use carries potential for harm, causing skin breakdown in up to approximately 4%. 35–38 Intermittent pneumatic compression has been shown to be highly effective in critically ill and stroke patients but would likely prove impractical for many patients with ALS who retain residual mobility as these devices require large motors to cyclically inflate compression cuffs. 39–41

Routine practice in the UK dictates that nearly all hospital inpatients over 65, even without the presence of pathology, are given low-dose anticoagulation (typically LMWH) to reduce the risk of VTE. 13 The American College of Chest Physicians acknowledge that it is likely that immobile care-home patients have similar VTE risk to postacute care patients, but these patients are rarely given prophylaxis. 11 The reason for this is the high risk of bleeding, particularly intracranially, from falls when taking anticoagulants. Between 1% and 7% of patients per year receiving prophylactic dose of the DOAC apixaban experience significant bleeding events. 42 ALS is a condition associated with a high risk of falls, despite efforts to minimise their frequency using predictive calculators, and most clinicians do not institute routine anticoagulant or mechanical VTE prophylaxis. 43 One possible strategy could be to instigate pharmacological prophylaxis only in wheelchair-dependent patients at lower risk of falls.

One potential weakness of this study is that the hospital record database only included those admitted to hospital at some point in their disease course and not all patients diagnosed with ALS. It is, therefore, possible that those with ALS in this study had an inherently higher VTE risk than non-hospitalised individuals with ALS, for example, due to the presence of VTE inducing comorbidities precipitating admission. However, a study in Italy reported that 98% of patients with ALS are admitted to hospital at least once in their disease course. 44 We also mitigated this bias by calculating aHRs against a matched cohort of hospitalised patients, who were likely to have a similar level of inherent VTE risk (minus that caused by ALS). Therefore, our aHR result is felt to be generalisable to the majority of those with ALS in the UK. This study did not directly compare ALS with other causes of progressive paralysis. It is, therefore, possible that the increased risk of VTE seen in ALS might also be true of any other cause of paralysis. It was not possible to manually recheck coded diagnoses from the HES-APC as these data were not available. However, a meta-analysis investigating coding accuracy from 2004 to 2011 in this database estimated accuracy at 96.2% for primary diagnoses (the same diagnostic position used for this study). Furthermore, it is unlikely that an ALS diagnosis would be made lightly owing to its severity and rarity. Due to the limitations of record linkage, we were unable to investigate the previously reported, and intuitively plausible, increased risk factor of lower limb weakness in ALS as well as other specific ALS patient groups such as bulbar-onset and percutaneous gastrostomy-fed patients. Detailed phenotypic and staging information on patients with ALS was also not available. We were also unable to investigate the prevalence of incidental PE in this patient group, which requires further dedicated work.

Alongside our novel finding of higher risk in younger people hospitalised with ALS, this study suggests a more individualised balance of risks and benefits may need to be defined to minimise the rare, but potentially catastrophic complication of PE in ALS. It strengthens the case for a definitive randomised trial of routine VTE prophylaxis after a diagnosis of ALS, possibly comparing antithrombotic therapy, against either compression stockings or no intervention. If antithrombotic therapy reduced the risk of DVT by 80%, we estimate there would need to be 12 events and approximately 650 person-years of follow-up (alpha 0.05 and 80% power), so a multicentre study would be required.

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RG and MT contributed equally.

Contributors RG and MT codrafted the paper. RG, EJAM and MJG undertook the data extraction and statistical analysis. All authors interpreted the results and edited the final manuscript. RG is the study guarantor.

Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

Competing interests None declared.

Provenance and peer review Not commissioned; externally peer reviewed.

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A multiple case research design shifts the focus from understanding a single case to the differences and similarities between cases. Thus, it is not just conducting another (sec-ond, third, etc.) case study. Rather, it is the next step in developing a theory about fac-tors driving differences and similarities.
The Multiple Case Study Design
The multiple case study design is a valuable qualitative research tool in studying the links between the personal, social, behavioral, psychological, organizational, cultural, and environmental factors that guide organizational and leadership development. Case study research is essential for the in-depth study of participants' perspectives on ...
Three most important advantages of multiple case study and survey
Download scientific diagram | Three most important advantages of multiple case study and survey method from publication: Qualitative and Quantitative Research Methods in Management Science | It is ...
The case study approach
A case study is a research approach that is used to generate an in-depth, multi-faceted understanding of a complex issue in its real-life context. It is an established research design that is used extensively in a wide variety of disciplines, particularly in the social sciences. A case study can be defined in a variety of ways (Table.
The Multiple Case Study Design Methodology and Application for
The multiple case study design is a valuable qualitative research tool in studying the links between the personal, social, behavioral, psychological, organizational, cultural, and environmental factors that guide organizational and leadership development. Case study research is essential for the in-depth study of participants' perspectives on ...
Perspectives from Researchers on Case Study Design
Case study research is typically extensive; it draws on multiple methods of data collection and involves multiple data sources. The researcher begins by identifying a specific case or set of cases to be studied. Each case is an entity that is described within certain parameters, such as a specific time frame, place, event, and process.
Case Study Method: A Step-by-Step Guide for Business Researchers
The multiple case studies used in this article as an application of step-by-step guideline are specifically designed to facilitate these business and management researchers. This article presents an easy to read, practical, experience-based, step-by-step guided path to select, conduct, and complete the qualitative case study successfully. ...
Continuing to enhance the quality of case study methodology in health
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 ...
Doing Case Study Research Collaboratively: The Benefits for Researchers
The ten-member team was developed in mid-2019 to research the motivations and experiences of graduate-entry MNSc students enrolled in three universities and an Institute of Technology within Australasia and have published their findings in 2021 (Jarden et al., 2021; Macdiarmid et al., 2021b, 2021).The New Zealand team members were located within the North and South Island, and the Australian ...
Case Study
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 ...
PDF Chapter 3 Methodology: Multiple-Case Qualitative Study
Study. This longitudinal multiple-case study is qualitative in nature, with data collection lasting for more than a year. As this study set out to understand the experiences, feelings, emotions, conceptions, and understanding of students about their experi-ences, a qualitative research approach was adopted to "identify issues from the ...
5 Benefits of the Case Study Method
Through the case method, you can "try on" roles you may not have considered and feel more prepared to change or advance your career. 5. Build Your Self-Confidence. Finally, learning through the case study method can build your confidence. Each time you assume a business leader's perspective, aim to solve a new challenge, and express and ...
Single case studies vs. multiple case studies: A comparative study
This study attempts to answer when to write a single case study and when to write a multiple case study. It will further answer the benefits and disadvantages with the different types. The literature review, which is based on secondary sources, is about case studies. Then the literature review is discussed and analysed to reach a conclusion ...
A Multi-method Approach in Qualitative Research
Research Design Review has published articles on two special types of multiple-method qualitative research— case study and narrative research —each of which is a form of "case-centered" qualitative research, a term coined by Mishler (1996, 1999) and used by others (cf. Riessman, 2008) to denote a research approach that preserves the ...
10 Case Study Advantages and Disadvantages (2024)
Advantages. 1. In-depth analysis of complex phenomena. Case study design allows researchers to delve deeply into intricate issues and situations. By focusing on a specific instance or event, researchers can uncover nuanced details and layers of understanding that might be missed with other research methods, especially large-scale survey studies.
PDF A multiple case design for the investigation of information management
The multiple-case design was the best research design for this study, as it allowed the researcher to use best practices from the two international universities in order to develop a conceptual framework for the University of Johannesburg. The major benefit of using a multiple-case design was that multiple perspectives of the individuals
Advantages of the multiple case series approach to the study of
Advantages of the multiple case study design for theoretical development. As Willcutt et al. (2008) note, in addition to explaining the heterogeneity across the spectrum of disorders such as ASD, it is also important that current models account for the significant neuropsychological heterogeneity at the level of the individual. The evidence ...
The Advantages and Limitations of Single Case Study Analysis
Single case study analyses offer empirically-rich, context-specific, holistic accounts and contribute to both theory-building and, to a lesser extent, theory-testing. ... with a single unit of analysis, and an 'embedded' case design with multiple units of analysis (Yin, 2009: 50-52). The former, for example, would examine only the overall ...
The benefits of blockchain for digital certificates: A multiple case
The benefits analysed by the study can refer to why and how questions. Therefore, the case study approach is considered suitable for this research. Compared with single case analysis, multiple case analysis provides more robust findings with strength in replication logic [48].
Contributions of human cultures to biodiversity and ecosystem
According to our Review, biodiversity and cultural diversity are interdependent 177, forming social-ecological systems that generate multiple co-benefits to nature and human societies.Another ...
Venous thromboembolism risk in amyotrophic lateral sclerosis: a
Background Venous thromboembolism (VTE) can occur in amyotrophic lateral sclerosis (ALS) and pulmonary embolism causes death in a minority of cases. The benefits of preventing VTE must be weighed against the risks. An accurate estimate of the incidence of VTE in ALS is crucial to assessing this balance. Methods This retrospective record-linkage cohort study derived data from the Hospital ...

Multiple Case Studies

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Key Research Books and Articles on Multiple Case Study Methodology

Recent Dissertations Using Multiple Case Study Methodology

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Perspectives from Researchers on Case Study Design

What is a “case study” research design?

Qualitative Research with Case Studies

Mixed Methods Research with Case Studies

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Designing Survey Research

Case Study – Methods, Examples and Guide

Types of Case Study

Single-Case Study

Multiple-Case Study

Descriptive Case Study

Instrumental Case Study

Case Study Data Collection Methods

Observations

How to conduct Case Study Research

Examples of Case Study

Application of Case Study

Business and Management

Social Sciences

Law and Ethics

Purpose of Case Study

Advantages of Case Study Research

Limitations of Case Study Research

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Muhammad Hassan

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5 Benefits of Learning Through the Case Study Method

What Is the Harvard Business School Case Study Method?

5 Benefits of Learning Through Case Studies

2. Hone Your Decision-Making Skills

3. Become More Open-Minded

4. Enhance Your Curiosity

5. Build Your Self-Confidence

How to Experience the Case Study Method

About the Author

Research Design Review

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10 Case Study Advantages and Disadvantages

Case Study Advantages and Disadvantages

2. Holistic Understanding

3. Examination of rare and Unusual Phenomena

4. Helps Reveal the Experiences of Marginalzied Groups

5. Ideal in Situations where Researchers cannot Control the Variables

6. Supports the generation of new theories or hypotheses

7. Reveals the Unexpected

Disadvantages

2. Subjectivity in interpretation

3. Difficulty in replicating results

Comprehension Quiz for Students

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Advantages of the multiple case series approach to the study of cognitive deficits in autism spectrum disorder

1. Introduction

2.1. Participant population

2.2. Measures

2.2.1. Language

2.2.2. Perception

2.2.3. Memory

2.2.4. Executive function