Case Selection

Conceptual Overview and Discussion

The selection of cases is an essential part of the case study research design. Because of the intensive data collection methods in case study research, the number of research units can be very limited. Single-case designs examine one unit of a social phenomenon, while multiple-case designs compare 2 to 10 cases. This relatively limited amount of research units puts an emphasis on the researchers' justification of the selection of cases. In contrast to survey research, case study research samples are ideally selected strategically rather than randomly. Researchers need to select cases that give a maximum amount of information about the research objective at stake. For example, researchers look for cases that give a maximum opportunity to falsify hypotheses that are drawn from earlier research. Or they select cases that help to identify the specific conditions and characteristics of a phenomenon that has been characterized in only general terms.

The criteria for case selection depend on the type of research question: descriptive, exploratory, or explanatory. With a descriptive research question, the cases selected should give maximal information about the specific features and characteristics of a particular social phenomenon. With a single case study, researchers look for an average case; a case that is a typical example of a specific phenomenon. They may also select an extreme case; a case where the social phenomenon is visible in a very pronounced way or under extreme circumstances. By investigating such a case in depth, a detailed and elaborate description of the phenomenon is reached. A descriptive research question may also lead to a multiple-case study design, where a series of cases with common characteristics are studied. The researchers focus on describing the cases separately, rather than looking for common patterns and explanations. The specific features and characteristics of the cases are compared. Alexander George and Andrew Bennett refer to this type of (single and multiple) case study as ideographic configurative case study.

With an exploratory research question, researchers select cases that maximize the opportunities for developing hypotheses or theories that explain the social phenomenon at stake. Since this is an inductive research design, screening of the cases has to be based on empirical considerations. The researcher selects a single case that obviously differs from other instances of a social phenomenon—this is called a deviant case study. Or the researcher selects a case that seems not to fulfill theoretical expectations, with the aim to use the case for the purpose of developing additional theories—this is called a critical case study design. Another multiple-case [Page 62]study design with an exploratory character is the one George and Bennett call the building block theory. Researchers screen all instances of a social phenomenon for subclasses with similar characteristics. By systematically describing and comparing within these subclasses, subtheories may be developed that cover a part of the social phenomenon. These may be added to theories derived from different selections of groups.

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