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Bias in meta-analysis detected by a simple, graphical test

Asymmetry detected in funnel plot was probably due to true heterogeneity

Editor–Egger et al report that they "found bias in 38% of meta-analyses published in four leading journals."¹ This is misleading, at least insofar as our meta-analysis of inpatient geriatric consultations is concerned.²

Firstly, the bias observed in our meta-analysis was not a retrospective detection of bias, as one might infer from Egger et al’s statements. We knew that there was evidence of heterogeneity for the pooled effect estimates of geriatric consultation programmes and reported this finding.² Secondly, the asymmetry detected in the funnel plot of the meta-analysis of inpatient consultation programmes was probably due not to bias (distortion of true effect) but to true heterogeneity (true difference of effects between trials). We took the presence of heterogeneity as an opportunity to examine whether we could identify the programme elements that might have resulted in the observed effect differences between . . . [Full text of this article]

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Relevant Article

Bias in meta-analysis detected by a simple, graphical test

Matthias Egger, George Davey Smith, Martin Schneider, and Christoph Minder
BMJ 1997 315: 629-634. [Abstract] [Full Text]

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