Outcome reporting bias (ORB) is a threat to validity of systematic reviews. Multivariate meta-analysis (MVMA) can potentially reduce the impact of ORB when outcomes are correlated. The aim of this study was to assess ORB in Cochrane systematic reviews of rheumatoid arthritis and to demonstrate how MVMA may examine its impact.
Reviews were assessed for ORB in relation to eight outcomes for rheumatoid arthritis using a nine-point classification system. Impact of ORB was assessed by comparing estimates from univariate meta-analysis and MVMA models.
ORB assessment was applied in 21 included reviews, and all contained missing data on at least one of the eight outcomes. ORB was highly suspected in 247 (22%) of the 1,118 evaluable outcomes from 155 assessable trials. MVMA and univariate results sometimes differed importantly. The maximum change in treatment effect estimate between MVMA and univariate meta-analysis approach was found to be 176% for one of the outcome considered.
ORB has the potential to affect the conclusions in meta-analyses. This could be avoided if trialists reported on all measured outcomes in full. If missing outcome data are unobtainable, MVMA is useful to examine the impact of missing outcomes and ORB on conclusions.