Qualitative Methods for the Study of Policy Diffusion: Challenges and Available Solutions

This article deals with the question whether and how processes of policy diffusion can be examined with qualitative methods. More specifically, how can qualitative methods address the “twin challenge of interdependence,” namely the challenge to identify diffusion, on the one hand, and the challenge to discriminate between mechanisms of diffusion, on the other? I argue, first, that there are three distinct qualitative techniques that can be used, namely cross‐case analysis (often based on systematic case selection), within‐case process tracing, and counterfactual reasoning. I demonstrate how these techniques can be adapted to the study of policy diffusion. Second, a combination of these methods is the best practice, since they are largely complementary in terms of the twin challenge of diffusion. The discussion draws on numerous illustrations from recent qualitative policy diffusion studies. The article closes with some suggestions for further methodological development in the study of policy diffusion, including the combination of quantitative and qualitative methods.