Academic journal article Political Research Quarterly

Case Selection Techniques in Case Study Research: A Menu of Qualitative and Quantitative Options

Academic journal article Political Research Quarterly

Case Selection Techniques in Case Study Research: A Menu of Qualitative and Quantitative Options

Article excerpt

How can scholars select cases from a large universe for in-depth case study analysis? Random sampling is not typically a viable approach when the total number of cases to be selected is small. Hence attention to purposive modes of sampling is needed. Yet, while the existing qualitative literature on case selection offers a wide range of suggestions for case selection, most techniques discussed require in-depth familiarity of each case. Seven case selection procedures are considered, each of which facilitates a different strategy for within-case analysis. The case selection procedures considered focus on typical, diverse, extreme, deviant, influential, most similar, and most different cases. For each case selection procedure, quantitative approaches are discussed that meet the goals of the approach, while still requiring information that can reasonably be gathered for a large number of cases.

Keywords: case study; case selection; qualitative methods; multimethod research

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Case selection is the primordial task of the case study researcher, for in choosing cases, one also sets out an agenda for studying those cases. This means that case selection and case analysis are intertwined to a much greater extent in case study research than in large-W cross-case analysis. Indeed, the method of choosing cases and analyzing those cases can scarcely be separated when the focus of a work is on one or a few instances of some broader phenomenon.

Yet choosing good cases for extremely small samples is a challenging endeavor (Gerring 2007, chaps. 2 and 4). Consider that most case studies seek to elucidate the features of a broader population. They are about something larger than the case itself, even if the resulting generalization is issued in a tentative fashion (Gerring 2004). In case studies of this sort, the chosen case is asked to perform a heroic role: to stand for (represent) a population of cases that is often much larger than the case itself. If cases consist of countries, for example, the population might be understood as a region (e.g., Latin America), a particular type of country (e.g., oil exporters), or the entire world (over some period of time). Evidently, the problem of representativeness cannot be ignored if the ambition of the case study is to reflect on a broader population of cases. At the same time, a truly representative case is by no means easy to identify. Additionally, chosen cases must also achieve variation on relevant dimensions, a requirement that is often unrecognized. A third difficulty is that background cases often play a key role in case study analysis. They are not cases per se, but they are nonetheless integrated into the analysis in an informal manner. This means that the distinction between the case and the population that surrounds it is never as clear in case study work as it is in the typical large-N cross-case study.

Despite the importance of the subject, and its evident complexities, the question of case selection has received relatively little attention from scholars since the pioneering work of Eckstein (1975), Lijphart (1971,1975), and Przeworski and Teune (1970). To be sure, recent work has noted the problem of sample bias and debated its sources and impact at great length (Achen and Snidal 1989; Collier and Mahoney 1996; Geddes 1990; King, Keohane, and Verba 1994; Rohlfing 2008; Sekhon 2004), but no solutions to this problem have been proffered beyond those implicit in work by Eckstein, Lijphart, and Przeworski and Teune.

In the absence of detailed, formal treatments, scholars continue to lean primarily on pragmatic considerations such as time, money, expertise, and access. They may also be influenced by the theoretical prominence of a given case. Of course, these are perfectly legitimate factors in case selection. Yet they do not provide a methodological justification for why case A might be preferred over case B. …

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