The present article aims to contribute to the debate on qualitative methods in policy evaluation. The central claim is that those methods are fundamental in order to uncover and refine our knowledge on why programmes work. The article starts with a brief review of the literature on causal mechanisms, providing a basic definition of mechanisms and discussing their utility in policy evaluation. The article proceeds by defending the methodological advantage of case studies for the formulation of new theories and then presents process tracing as a rigorous methods for drawing within-case inferences. An extended example of a local development programme is used to illustrate the method.
Keywords: Process Tracing, Causal Mechanisms, Qualitative Methods, Realistic Evaluation, Theory-Driven Evaluation, Local Development