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Adequacy and reporting of allocation concealment: review of recent trials published in four general medical journals

BMJ 2005; 330 doi: (Published 05 May 2005) Cite this as: BMJ 2005;330:1057
  1. Catherine Hewitt, PhD student (,
  2. Seokyung Hahn, assistant professor2,
  3. David J Torgerson, director1,
  4. Judith Watson, research fellow1,
  5. J Martin Bland, professor of health statistics1
  1. 1 York Trials Unit, Department of Health Sciences, University of York, York YO10 5DD,
  2. 2 Medical Research Collaborating Center, Seoul National University Hospital/College of Medicine, Seoul 110-744, Korea
  1. Correspondence to: C Hewitt
  • Accepted 28 January 2005


In randomised controlled trials, allocation concealment (separating the process of randomisation from the recruitment of participants) is important for rigorously designed trials.14 In 1996 many major medical journals adopted the CONSORT statement (whereby researchers have to include a short checklist of essential items and a flow diagram when reporting trials),5 and this move encouraged the reporting of allocation concealment. We reviewed the prevalence of adequate allocation concealment and its association with the statistical significance of trial results.

Methods and results

We searched by hand four general medical journals (the BMJ, JAMA, the Lancet, and the New England Journal of Medicine) to identify randomised controlled trials published from January 2002 to December 2002. We included articles if the authors reported that participants were randomised and if the trial was published as a full report with the results of the main analyses. We categorised articles according to whether allocation concealment was adequate (the person who executed the allocation sequence was different from the person who recruited …

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