CONTROVERSY OF ORAL-CONTRACEPTIVES AND RISK OF RHEUMATOID-ARTHRITIS -METAANALYSIS OF CONFLICTING STUDIES AND REVIEW OF CONFLICTING METAANALYSES WITH SPECIAL EMPHASIS ON ANALYSIS OF HETEROGENEITY

The authors analyze the heterogeneity present in the combined results of past observational studies that investigated the association betwee n oral contraceptive use and rheumatoid arthritis. The authors also ev aluate discrepancies among meta-analyses that focus on the same relati on. Of the 15 initially reviewed studies, 10 were selected for this me ta-analysis, which also includes a qualitative summary of study charac teristics and a critical appraisal of study quality. The authors used the direct method to combine the study results when there was no evide nce of heterogeneity and the DerSimonian-Laird method when heterogenei ty was present. Using a meta-regression to assess the sources of heter ogeneity, the authors weighted summary estimates by sample size and un dertook a sensitivity analysis. There was a strong indication of heter ogeneity when combining all studies (chi(2) = 29.34, p = 0.00060) with the source of controls explaining most of the heterogeneity. The most important factor in explaining the differences among the overall summ ary estimates given by the meta-analyses is that different effect esti mates had been selected for the same studies. There is no conclusive e vidence of a protective effect of oral contraceptives on the risk of d eveloping rheumatoid arthritis, Consensus is needed on how meta-analys es of observational studies should be conducted.