Combining process tracing and synthetic control method: Bridging two ways of making causal inference in evaluation research

This article discusses potential ways of combining two methods of evaluation in single-case studies: the synthetic control method and the process tracing method. Both are designed to examine certain events/programmes that take place in given cases but view these events/programmes from different causal perspectives. Seeing an event/programme as a cause, synthetic control estimates its impact on one or more outcomes. Conversely, starting from a certain outcome, process tracing uncovers the causes responsible. One can start from the causal explanation reached via one of the two methods and then proceed to examine that explanation through the other method. Once the causes of an outcome are traced via a process tracing analysis, that account can be validated by estimating the effects of those causes via synthetic control. Equally, once the impact of a certain event is estimated through synthetic control, causal mechanisms traceable via process tracing can be exploited to refine that impact evaluation.