Selective outcome reporting in root coverage randomized clinical trials

Background Outcome discrepancies between protocols and respective publications represent a concerning bias. The purpose of this study was to assess the prevalence of selective outcome reporting (SOR) in root coverage randomized clinical trials (RCTs). Methods Published root coverage RCTs (July 2005 to March 2020) were included if a corresponding protocol could be identified in a public registry. Discrepancies between protocol and its correspondent publication(s) were compared regarding primary and secondary outcomes and other study characteristics. Associations between trial characteristics and SOR were evaluated. Results Forty four studies (54 publications) were included. The majority of studies (77.3%) were retrospectively registered. SOR was frequent (40.9% of trials) and consisted of primary outcome downgrade (22.7%); secondary outcome upgrade (11.4%); new primary outcome introduced in publication (25%); protocol primary outcome omitted from publication (13.6%) and discrepancy in primary outcome timing (18.2%). SOR was unclear in 20.5% of studies and favoured statistical significance in 12 studies (27.3%). SOR was significantly associated with study significance (p < 0.001) and unclear outcome definition in the publication (p < 0.001). Only a third (32.8%) of primary outcomes were completely defined. Conclusions The present study identified high prevalence of SOR in root coverage RCTs.