Historical Process Tracing

Historical process tracing is a within-case method for establishing causation by following a hypothesized mechanism step by step through the sequence of events that links a cause to an outcome. Systematized for the social sciences by Alexander George and Andrew Bennett and refined by James Mahoney, the approach treats history not as a source of correlations across cases but as a chain of intervening steps whose presence or absence can confirm or refute rival explanations. Instead of asking whether a cause covaries with an outcome across many units, process tracing asks whether the connecting mechanism actually operated in the case at hand, examining diagnostic pieces of evidence, causal-process observations, against the predictions of competing hypotheses. Drawing on the logic of Bayesian updating and on tests such as the hoop test and the smoking-gun test, it offers a disciplined way to leverage rich qualitative detail for strong causal inference in single cases and small comparisons typical of historical institutionalism.