Bridging Theory and Intervention: The Need for Proof-of-Principle RCTs to Advance Health Psychology Interventions

A big part of intervention development is testing before implementation. Bridging the gap between observational findings gained from interviews, focus groups, and correlational studies, theoretical science-focused evidence from experiments, and the gold-standard in intervention testing in large-scale randomized controlled trials (RCTs) remains a challenge in behaviour change intervention development. This article introduces Proof-of-Principle RCTs (PoP-RCTs) as an intermediate step in bridging this gap. PoP-RCT are designed to test whether the intervention changes specific targeted mechanisms of action (MoAs), thus having the potential to change the behaviours targeted, before instigating larger trials. By focusing on the MoAs, PoP-RCTs offer a critical step that ensures theoretical assumptions are validated using experimental methodology, improving the overall rigor of intervention development. Practical case studies are included to illustrate real-world application of PoP-RCTs in health psychology. Highlighting their role in refining interventions before full-scale RCT testing, in work on recovery of activity after stroke. Following interview studies, evidence was obtained that greater perceived control predicted better and faster recovery. These studies were followed by experimental testing of interventions to enhance perceived control, in studies we now term PoP-RCTs. Having demonstrated that the interventions could change perceived control, a full trial found that they were effective in increasing activity.Taken together, we think PoP-RCTs are already an implicit part of intervention development. Proposing this as an explicitly labelled step between experiments and RCTs, could improve effectiveness/efficacy and increase intervention success.