How is process tracing applied in health research? A systematic scoping review.

Complex health system questions often have a case study (such as a country) as the unit of analysis. Process tracing, a method from policy studies, is a flexible approach for causal analysis within case studies, increasingly used in applied health research. The aim of this study was to identify the ways in which process tracing methods have been used in health research, and provide insights for best practice. We conducted a systematic scoping review of applied studies purporting to use process tracing methods in health research contexts. We examined the range of studies and how they conducted and reported process tracing. We found 84 studies published from 2011 to 2023. Studies were categorised into two groups: those with greater methodological description (n = 19 studies) and those with less methodological description (n = 65 studies). A majority of studies were focused on public health and health policy with around half of studies focused on low and middle income countries. Of those 19 studies that provided greater methodological description eight studies featured four areas of good practice: (1) reporting the development of a mechanistic theory and making it explicit; (2) linking empirical material collected to the mechanistic theory; (3) clearly presenting the causal mechanism tracing; and (4) reporting how consideration of counterfactuals or evidence of alternatives within the study were analysed in practice. The review demonstrates the rapid take-up of process tracing to generate theory and evidence to support a better understanding of causal mechanisms in complex health research. To support future studies in conducting and reporting process tracing, we provide emergent recommendations.