What can causal process tracing offer to policy studies? A review of the literature

Causal process tracing (CPT) has emerged as an important method of causal inference in qualitative social science research, most notably in case study research designs. There is now a considerable literature on the aims, philosophical groundings, and methods of process tracing. This paper reviews the CPT literature to assess what new directions it may suggest for policy studies. The first part of the paper sets out the methodological advantages CPT offers in building and testing theories of policy change, most notably in supporting a theoretical pluralism to address the problem of complexity in policy studies. Building on recent scholarship across the social sciences, the second part examines step by step the recently minted "best practice" for undertaking CPT in policy studies. This part includes discussion of the possible pitfalls of CPT as a method; common errors involved in its use are set out and minimization strategies offered. In particular, while acknowledging the usefulness of Bayesian tests for causality as heuristic devices, we emphasize the limitations of applying such tests in practice. Possible correctives are suggested. The final part of the paper speculates more generally on the potential of CPT to improve our investigation of patterns of policy change over time.