The contribution of process tracing to theory-based evaluations of complex aid instruments

This article focuses on methodological challenges in evaluating complex program aid interventions like budget support. We show that recent innovations in process-tracing methodology can help solve the identified challenges and increase the strength of causal inference made when using case studies in demanding settings. For the specific task of evaluating the governance effectiveness of budget support interventions, we developed a more fine-grained causal mechanism for a sub-set of the comprehensive program theory of budget support. Moreover, based on the informal use of Bayesian logic, we have elaborated on how to increase the conclusiveness of empirical evidence for one part of the theorized causal mechanism. We argue that by establishing an explicit theorized mechanism prior to empirical research and by critically judging our evidence according to an informal Bayesian logic we can remedy some of the problems at hand in much case-study research and increase the inferential leverage in complex within-case evaluation studies.