The following is a modified excerpt from Applied Qualitative Research Design: A Total Quality Framework Approach (Roller & Lavrakas, 2015, pp. 295-298).

Janet Salmons posted an article “Case Studies: What Types Get Published?” in which she discusses her review of over 100 articles published in 2017 with “case study” in the title. She finds that the majority of these articles do “not include any discussion of the type of case study or specific methodological foundations” and indeed “the term ‘case study’ is being used to broadly describe a study that is conducted in a particular setting, such as a school or organization.”

Salmons mentions the work of Robert Yin and Robert Stake. The typologies of Yin (2014) and Stake (1995) are “two key approaches” in case study research that “ensure that the topic of interest is well explored, and that the essence of the phenomenon is revealed” (Baxter & Jack, 2008, p. 545). Yin (2014) outlines four fundamental types of case studies on the basis of the number of cases and units of analysis in the study design. Specifically, Yin’s typology consists of two types of single-case designs – a type with one unit of analysis (Type 1) and a type with multiple units of analysis (Type 2) – and two types of multiple-case designs – those with one unit of analysis (Type 3) and those with more than one (Type 4). Yin believes that theory development is “highly desired” in case study design and therefore selecting cases for a multiple-case design, for example, involves choosing cases that are expected to return results that support or challenge a theoretical proposition or construct.

Where Yin (2014) emphasizes theoretical development and the ability to say something beyond the specific cases studied, Stake (2006) asserts that “the power of case study is its attention to the local situation, not in how it represents other cases in general” (p. 8). Stake (1995) divides case studies into three types: intrinsic – a single case (an individual, group, organization, event, or other entity) that is important in its own right, not necessarily because of its potential predictive theoretical powers; instrumental – a single case where the focus is on going beyond the case to understand a broader phenomenon of interest; and collective – a multiple case version of instrumental where the focus is on learning about a phenomenon. Unlike Yin, Stake is not linking his case studies to the idea of testing preconceived theories but rather to the idea of using the peculiarities of any particular case to illuminate the phenomenon and magnify the understanding of the research topic.

An overarching differentiator in the Yin and Stake typologies is the extent to which case study outcomes are intended to tell the researcher something that is solely about the case itself – that is, the outcomes are “internalized” to the particular case – or the outcomes are intended to tell the researcher something beyond the case, either by facilitating theory development and/or enlightening the researcher’s understanding of a broader phenomenon – that is, the outcomes are “externalized” to situations outside the case.

This internal-external classification, and its relationship to the Yin and Stake typologies, is shown below.

In this internal-external classification, an intrinsic case study as defined by Stake, with its emphasis on what can be learned about the specific case itself, is classified as an internal type of design because the research findings will only be used to inform that specific case. An example of an internal case study is research that a healthcare organization might conduct to investigate its new patient-referral program to inform their need for new social media solutions.

Stake’s instrumental and collective case study types as well as Yin’s case study designs (i.e., types 1-4), with their emphasis on projecting case study results to something outside the case (i.e., a theory or phenomenon), are classified as external case study designs because the researcher’s primary focus is on extending the outcomes beyond the specific cases(s). For example, an external case study might be conducted with one or two state government department(s) to understand the impact of a newly-implemented, more restrictive sick-leave policy on all state employees.

The internal-external classification is one way to think broadly about case study design. Regardless of the design model, however, case study researchers would do well to clearly articulate, as Salmons states, the “methodological foundations” of their designs.

Baxter, P., & Jack, S. (2008). Qualitative case study methodology: Study design and implementation for novice researchers. The Qualitative Report, 13(4), 544–559.

Roller, M. R., & Lavrakas, P. J. (2015). Applied qualitative research design: A total quality framework approach. New York: Guilford Press.

Stake, R. E. (1995). The art of case study research. Thousand Oaks, CA: Sage Publications.

Yin, R. K. (2014). Case study research: Design and methods (5th ed.). Thousand Oaks, CA: Sage Publications.

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