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February 27, 2013

Emergence of Large Treatment Effects From Small Trials

Author Affiliations

Letters Section Editor: Jody W. Zylke, MD, Senior Editor.

Author Affiliations: Teesside University, Middlesbrough, United Kingdom (Dr Batterham; a.batterham@tees.ac.uk); and Auckland University of Technology, Auckland, New Zealand (Dr Hopkins).

JAMA. 2013;309(8):768-769. doi:10.1001/jama.2012.208828

To the Editor: After analyzing forest plots from the Cochrane Database of Systematic Reviews, Dr Pereira and colleagues1 reported that most large treatment effects emerged from small trials. This finding mirrors what epidemiologists and medical statisticians have known for years: large treatment effects appear in most meta-analyses as asymmetry in the scatter of points on funnel plots of effect magnitude against standard error.

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