Abbreviated and comprehensive literature searches led to identical or very similar effect estimates: meta-epidemiological study

Abstract Objective : Assessing the agreement of treatment effect estimates from meta-analyses based on abbreviated or comprehensive literature searches. Study Design and Setting : Meta-epidemiological study. We abbreviated 47 comprehensive Cochrane review searches and searched MEDLINE/Embase/CENTRAL alone, in combination, with/without checking references (658 new searches). We compared one meta-analysis from each review with recalculated ones based on abbreviated searches. Results : The 47 original meta-analyses included 444 trials (median 6 per review [IQR 3–11]) with 360045 participants (median 1371 per review [IQR 685–8041]). Depending on the search approach, abbreviated searches led to identical effect estimates in 34%–79% of meta-analyses, to different effect estimates with the same direction and level of statistical significance in 15%–51%, and to opposite effects (or effects could not be estimated anymore) in 6%–13%. The deviation of effect sizes was zero in 50% of the meta-analyses and in 75% not larger than 1.07-fold. Effect estimates of abbreviated searches were not consistently smaller or larger (median ratio of odds ratio 1 [IQR 1–1.01]) but more imprecise (1.02–1.06-fold larger standard errors). Conclusion : Abbreviated literature searches often led to identical or very similar effect estimates as comprehensive searches with slightly increased confidence intervals. Relevant deviations may occur.