Process Tracing

Covariations have important limitations as sources of causal inference, whether these covariations are established by statistical methods or by congruence methods in case studies. Because of these limitations, philosophers of science and social science methdologists have given increasing emphasis in the last two decades to "causal mechanisms," or the causal processes and intervening variables through which causal or explanatory variables produce causal effects, as a second basis for causal inferences, and to process tracing as a method for identifying and testing causal mechanisms. This paper first looks at some of the philosophy science issues related to process tracing, including the roles of causal effects and causal mechanisms in causal explanation and the logic of process tracing. It then looks at how process tracing relates to common misunderstandings of case study methods, such as those on the "degrees of freedom problem" and the limitations of Mills' Methods. The paper then discusses the inductive and theory-testing uses of process tracing, and it concludes with observations on the limits as well as the strengths of process tracing.