More than one-third of systematic reviews did not fully report the adverse events outcome

The aim of the study was to assess the risk for adverse events reporting bias in systematic reviews of health care interventions registered to PROSPERO.

This study was a retrospective cohort study. Systematic review protocols in PROSPERO were screened and included if they focused on a health care intervention and listed an adverse event as either a primary or secondary outcome. The included systematic reviews were assessed to determine the completeness of reporting for the adverse event outcomes. Any discrepancies in reporting between protocol and review were recorded.

Of 1,376 protocols for systematic reviews sifted, only 524 (38%) listed adverse events outcomes. One hundred eighty-six protocols were published in 2017 and 2018, of which 146 were included in our analysis. Among the included systematic reviews, 65% (95/146) fully reported the adverse event outcomes as intended by the protocol, 8% (12/146) entirely excluded the adverse event outcome, and the remaining 27% (39/146) either partially reported or changed the adverse event outcomes.

Sixty-two percent of reviews did not mention adverse events in their protocol, and 35% of PROSPERO-registered systematic reviews had discrepant outcome reporting between the protocol and publication. The findings suggest a need for the encouraged use of harms reporting guidelines and further research into adverse events reporting bias.