Selective outcome reporting in obesity clinical trials: a cross-sectional review

Selective outcome reporting is a form of bias resulting from discrepancies between outcomes presented in a trial's registration and the published report. We investigate this selective bias in obesity clinical trials. A PubMed search was conducted to identify randomized controlled trials (RCTs) published in four obesity journals from 2013 to 2015. Primary, secondary and tertiary outcomes were recorded for each trial and compared to pre-specified outcomes in each trial's registration. Of the 392 identified articles, 142 were included in the final analysis; 22 (15%) RCTs demonstrated major outcome discrepancies between registration and publication: No primary outcomes were demoted to a secondary or tertiary outcome; 14 (36.84%) primary outcomes were omitted; 14 (36.84%) primary outcomes were added: 5 (13.16%) secondary outcomes were upgraded to primary outcomes; and timing of assessment for a primary outcome changed 5 (13.16%) times. Out of the 63 prospectively registered studies, 53 had no discrepancies. A total of 76 of the studies (29.80%) were unregistered or did not have an associated registration number. Our results suggest that selective outcome reporting may be a concern in obesity clinical trials. As selective outcome reporting may distort clinical findings and limit outcomes in systematic reviews, we encourage trialists and journal editors to work towards solutions to mitigate this issue.