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Ewald, Hannah; Klerings, Irma; Wagner, Gernot; Heise, Thomas L.; Dobrescu, Andreea Iulia; Armijo-Olivo, Susan; Stratil, Jan M.; Lhachimi, Stefan K.; Mittermayr, Tarquin; Gartlehner, Gerald; Nussbaumer-Streit, Barbara; Hemkens, Lars G. (2020): Abbreviated and comprehensive literature searches led to identical or very similar effect estimates: a meta-epidemiological study. In: Journal of Clinical Epidemiology, Vol. 128: pp. 1-12
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Abstract

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.