A third of systematic reviews changed or did not specify the primary outcome: a PROSPERO register study

J Clin Epidemiol. 2016 Nov;79:46-54. doi: 10.1016/j.jclinepi.2016.03.025. Epub 2016 Apr 11.

Abstract

Objectives: To examine outcome reporting bias of systematic reviews registered in PROSPERO.

Study design and setting: Retrospective cohort study. The primary outcomes from systematic review publications were compared with those reported in the corresponding PROSPERO records; discrepancies in the primary outcomes were assessed as upgrades, additions, omissions, or downgrades. Relative risks (RRs) and 95% confidence intervals (CI) were calculated to determine the likelihood of having a change in primary outcome when the meta-analysis result was favorable and statistically significant.

Results: Ninety-six systematic reviews were published. A discrepancy in the primary outcome occurred in 32% of the included reviews and 39% of the reviews did not explicitly specify a primary outcome(s); 6% of the primary outcomes were omitted. There was no significant increased risk of adding/upgrading (RR, 2.14; 95% CI: 0.53, 8.63) or decreased risk of downgrading (RR, 0.76; 95% CI: 0.27, 2.17) an outcome when the meta-analysis result was favorable and statistically significant. As well, there was no significant increased risk of adding/upgrading (RR, 0.89; 95% CI: 0.31, 2.53) or decreased risk of downgrading (RR, 0.56; 95% CI: 0.29, 1.08) an outcome when the conclusion was positive.

Conclusions: We recommend review authors carefully consider primary outcome selection, and journals are encouraged to focus acceptance on registered systematic reviews.

Keywords: Bias; Methodology; Outcome reporting bias; Quality; Reporting; Systematic reviews.

MeSH terms

  • Bias
  • Cohort Studies
  • Epidemiologic Research Design*
  • Humans
  • Outcome Assessment, Health Care / methods*
  • Outcome Assessment, Health Care / statistics & numerical data*
  • Registries / statistics & numerical data*
  • Retrospective Studies
  • Review Literature as Topic*
  • Risk