Geddes Barbara, "How the Cases You Choose Affect the Answers You Get: Selection Bias in Comparative Politics", Political Analysis, Vol. 2, 1990, , pp. 131-150.

Abstract

One of the most durable conventions in the field of comparative politics is the selection of cases for study on the dependent variable. That is, if we want to understand something, fore example, revolution, we select one or more occurrences and subject them to scrutiny. This article demonstrates how the selection of cases for study on the basis of outcomes on the dependent variables biases conclusions. It first lays out the logic of explanation and shows how it is violated when only cases that have achieved the outcome of interest are studied. It then examines three well known and highly regarded studies in the field of comparative politics, comparing the conclusions researched in the original work with a test of the arguments on cases sleeted without regard for their position on the dependent variable. In each instance, conclusions based on the uncorrected sample differ from the original conclusions.

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