Comparison of Estimates between Cohort and Case–Control Studies in Meta-Analyses of Therapeutic Interventions: A Meta-Epidemiological Study

BACKGROUND: Observational studies are increasingly being used for assessing therapeutic interventions. Case–control studies are generally considered to have greater risk of bias than cohort studies, but we lack evidence of differences in effect estimates between the 2 study types. We aimed to compare estimates between cohort and case–control studies in meta-analyses of observational studies of therapeutic interventions by using a meta-epidemiological study. METHODS: We used a random sample of meta-analyses of therapeutic interventions published in 2013 that included both cohort and case–control studies assessing a binary outcome. For each meta-analysis, the ratio of estimates (RE) was calculated by comparing the estimate in case–control studies to that in cohort studies. Then, we used random-effects meta-analysis to estimate a combined RE across meta-analyses. An RE < 1 indicated that case–control studies yielded larger estimates than cohort studies. RESULTS: The final analysis included 23 meta-analyses: 138 cohort and 133 case–control studies. Treatment effect estimates did not significantly differ between case–control and cohort studies (combined RE 0.97 [95% CI 0.86–1.09]). Heterogeneity was low, with between–meta-analysis variance τ(2) = 0.0049. Estimates did not differ between case–control and prospective or retrospective cohort studies (RE = 1.05 [95% CI 0.96–1.15] and RE = 0.99 [95% CI, 0.83–1.19], respectively). Sensitivity analysis of studies reporting adjusted estimates also revealed no significant difference (RE = 1.03 [95% CI 0.91–1.16]). Heterogeneity was also low for these analyses. CONCLUSION: We found no significant difference in treatment effect estimates between case–control and cohort studies assessing therapeutic interventions.