Case Study

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American Political Science Review

Vol. 98, No. 2

May 2004

What Is a Case Study and What Is It Good for?
JOHN GERRING
Boston University

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his paper aims to clarify the meaning, and explain the utility, of the case study method, a method often practiced but little understood. A “case study,” I argue, is best defined as an intensive study of a single unit with an aim to generalize across a larger set of units. Case studies rely on the same sort of covariational evidence utilized in non-case study research. Thus, the case study method is correctly understood as a particular way of defining cases, not a way of analyzing cases or a way of modeling causal relations. I show that this understanding of the subject illuminates some of the persistent ambiguities of case study work, ambiguities that are, to some extent, intrinsic to the enterprise. The travails of the case study within the discipline of political science are also rooted in an insufficient appreciation of the methodological tradeoffs that this method calls forth. This paper presents the familiar contrast between case study and non-case study work as a series of characteristic strengths and weaknesses—affinities— rather than as antagonistic approaches to the empirical world. In the end, the perceived hostility between case study and non-case study research is largely unjustified and, perhaps, deserves to be regarded as a misconception. Indeed, the strongest conclusion to arise from this methodological examination concerns the complementarity of single-unit and cross-unit research designs. tion of work generated by the discipline, the case study method is held in low regard or is simply ignored. Even among its defenders there is confusion over the virtues and vices of this ambiguous research design. Practitioners continue to ply their trade but have difficulty articulating what it is that they are doing, methodologically speaking. The case study survives in a curious methodological limbo. How can we understand the profound disjuncture that exists between the case study’s acknowledged contributions to political science and its maligned status within the discipline? If case studies are methodologically flawed, why do they persist? The paper is divided into two parts. The first part focuses on matters of definition. I argue that for methodological purposes a case study is best defined as an in-depth study of a single unit (a relatively bounded phenomenon) where the scholar’s aim is to elucidate features of a larger class of similar phenomena. It is demonstrated that case studies rely on the same sort of covariational evidence utilized in non-case study research. Thus, the case study method is correctly understood as a particular way of defining cases, not a way of analyzing cases or a way of modeling causal relations. I show, finally, that this understanding of the subject illuminates some of the persistent ambiguities of case study work, ambiguities that are, to some extent, intrinsic to the enterprise. In the second part of the paper I proceed to examine the contrast between case study and non-case study work. The central argument here is that the differences between these two genres are best understood as characteristic strengths and weaknesses—affinities—rather than antagonistic approaches to the empirical world. Tradeoffs, rather than dichotomies, characterize the ongoing case study/non-case study debate.

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he case study occupies a vexed position in the discipline of political science. On the one hand, methodologists generally view the case study method with extreme circumspection (Achen and Snidal 1989; King, Keohane, and Verba 1994; Lieberson [1991] 1992, 1994; Njolstad 1990). A work that focuses its attention on a single example of a broader phenomenon is apt to be described as a “mere” case study. At the same time, the discipline continues to produce a vast number of case studies, many of which have entered the pantheon of classic works (Allen 1965; Allison...
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