Case Studies and Theory Development in the Social Sciences - Alexander L. George [46]
Finally, a study that includes many cases may allow for several different types of comparisons. One case may be most similar to another and both may be least similar to a third case. As noted below, case selection is an opportunistic as well as a structured process—researchers should look for whether the addition of one or a few cases to a study might provide useful comparisons or allow inferences on additional types of cases.
Task Three: Case Selection
Many students in the early stages of designing a study indicate that they find it difficult to decide which cases to select. This difficulty usually arises from a failure to specify a research objective that is clearly formulated and not overly ambitious. One should select cases not simply because they are interesting, important, or easily researched using readily available data. Rather, case selection should be an integral part of a good research strategy to achieve well-defined objectives of the study. Hence, the primary criterion for case selection should be relevance to the research objective of the study, whether it includes theory development, theory testing, or heuristic purposes.
Cases should also be selected to provide the kind of control and variation required by the research problem. This requires that the universe or subclass of events be clearly defined so that appropriate cases can be selected. In one type of comparative study, for example, all the cases must be instances of the same subclass. In another type of comparative study that has a different research objective, cases from different subclasses are needed.
Selection of a historical case or cases may be guided by a typology developed from the work in Tasks One and Two. Researchers can be somewhat opportunistic here—they may come across a pair of well-matched before-after cases or a pair of cases that closely fit “most similar” or “least similar” case research designs. They may also come upon cases that have many features of a most- or least-likely case, a crucial case, or a deviant case.
Often researchers begin their inquiry with a theory in search of a test case or a case in search of a theory for which it is a good test.176 Either approach is viable, provided that care is taken to prevent case selection bias and, if necessary, to study several cases that pose appropriate tests for a candidate theory once one is identified. Often, the researcher might start with a case that interests her, be drawn to a candidate theory, and then decide that she is more interested in the theory than in the case and conclude that the best way to study the theory is to select several cases that may not include the case with which the inquiry began. Some such iteration is usually necessary—history may not provide the ideal kind of cases to carry out the tests or heuristic studies that a research program most needs at its current stage of development.
Important criticisms have been made of potential flaws in case selection in studies with one or a few cases; such concerns are influenced by the rich experience of statistical methods for analyzing a large-N. David Collier and James Mahoney have taken issue with some widespread concerns about selection bias in small studies; we note four of their observations. 177 They question the assertion that selection bias in case studies is potentially an even greater problem than is often assumed (that it may not just understate relationships—the standard statistical problem—but may overstate them). They argue that case study designs with no variance in the dependent variable do not inherently represent a selection bias problem. They emphasize that case study researchers sometimes have good reasons to narrow the range of cases studied, particularly to