Selective outcome reporting in trials of behavioural health interventions in health psychology and behavioural medicine journals: a review

Selective outcome reporting can result in overestimation of treatment effects, research waste, and reduced openness and transparency. This review aimed to examine selective outcome reporting in trials of behavioural health interventions and determine potential outcome reporting bias. A review of nine health psychology and behavioural medicine journals was conducted to identify randomised controlled trials of behavioural health interventions published since 2019. Discrepancies in outcome reporting were observed in 90% of the 29 trials with corresponding registrations/protocols. Discrepancies included 72% of trials omitting prespecified outcomes; 55% of trials introduced new outcomes. Thirty-eight percent of trials omitted prespecified and introduced new outcomes. Three trials (10%) downgraded primary outcomes in registrations/protocols to secondary outcomes in final reports; downgraded outcomes were not statistically significant in two trials. Five trials (17%) upgraded secondary outcomes to primary outcomes; upgraded outcomes were statistically significant in all trials. In final reports, three trials (7%) omitted outcomes from the methods section; three trials (7%) introduced new outcomes in results that were not in the methods. These findings indicate that selective outcome reporting is a problem in behavioural health intervention trials. Journal- and trialist-level approaches are needed to minimise selective outcome reporting in health psychology and behavioural medicine.