Process tracing and Bayesian updating for impact evaluation

This article introduces Contribution Tracing, a rigorous "quali-quantitative" method inspired by process tracing and Bayesian updating.

Commissioners of impact evaluation often emphasise assessing the contribution of interventions to outcomes, but current theory-based approaches can lack guidance on data collection and assessment. Contribution tracing provides explicit criteria for evaluators to collect data and measure confidence in their findings, enhancing theory-based approaches by reducing confirmation bias, improving theories of change, and increasing transparency and credibility.

An impact evaluation of Ghana's Universal Health Care campaign is provided as an example of the use of the method.