Making process evaluations more explanatory - key opportunities to advance implementation research

Process evaluation of implementation strategies is increasingly common, but a review by Bracci et al. showed that room for improvement exists. In this contribution, we complement their recommendations by ideas on the design of process evaluations. Process evaluations are meant to provide explanations for why implementation strategies were effective, or not effective. Therefore, they are best guided by theory or frameworks, but the frequent focus on intervention acceptability reflects a lack of imagination on moderators and mediators that influence outcomes. Intervention fidelity is relevant in all process evaluations. Meaningful synthesis of process evaluation studies requires a homogeneous outcome, such as uptake of practices.