Open Access

Objectives The objective of this study was to assess the agreement of treatment effect estimates from meta-analyses based on abbreviated or comprehensive literature searches. Study Design and Setting This was a 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 [interquartile range (IQR) 3–11]) with 360045 participants (median 1,371 per review [IQR 685–8,041]). 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.