Post-print: Assessing risk of contamination in psychological therapy trial protocols

We developed and piloted a simple framework, to help people identify contamination risk when writing protocols for psychological therapy trials. Contamination means people in the control arm getting the treatment, or aspects of the treatment, intended for people in the intervention arm. We tested the framework out on 100 trial protocols registered on the ISRCTN trial registry (isrctn.com). We found that only 14 out of the 100 protocols we looked at had a potential risk of contamination via any of the sources identified in the framework. Most of these trial protocols had already identified the potential contamination risk and had put in place appropriate design adaptations to help guard against the risk.