Clinical Trial Data is hidden; this bias crucially invalidates many meta-analyses


“Hart and colleagues incorporated unpublished evidence into existing meta-analyses of nine drugs approved by the US Food and Drug Administration in 2001 and 2002.1 These reanalyses produced identical estimates of drug efficacy in just three of 41 cases (7%); in the remaining cases, estimates of drug efficacy were evenly split between more (19/41) and less (19/41). It is sometimes assumed that incorporation of missing data will reduce estimates of drug benefits, but this study shows that “publication bias” can cut both ways.”

http://www.bmj.com/content/344/bmj.d8158
BMJ 2012

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