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Int J Epidemiol. 2011 Oct;40(5):1280-91. doi: 10.1093/ije/dyr095. Epub 2011 Sep 8.

Magnitude of effects in clinical trials published in high-impact general medical journals.

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  • 1Clinical Trials and Evidence-Based Medicine Unit, Department of Hygiene and Epidemiology, University of Ioannina School of Medicine, Ioannina, Greece.



Prestigious journals select for publication studies that are considered most important and informative. We aimed to examine whether high-impact general (HIG) medical journals systematically demonstrate more favourable results for experimental interventions compared with the rest of the literature.


We scrutinized systematic reviews of the Cochrane Database (Issue 4, 2009) and meta-analyses published in four general journals (2008-09). Eligible articles included ≥1 binary outcome meta-analysis(es) pertaining to effectiveness with ≥1 clinical trial(s) published in NEJM, JAMA or Lancet. Effect sizes in trials from NEJM, JAMA or Lancet were compared with those from other trials in the same meta-analyses by deriving summary relative odds ratios (sRORs). Additional analyses examined separately early- and late-published trials in HIG journals and journal-specific effects.


A total of 79 meta-analyses including 1043 clinical trials were analysed. Trials in HIG journals had similar effects to trials in other journals, when there was large-scale evidence, but showed more favourable results for experimental interventions when they were small. When HIG trials had less than 40 events, the sROR was 1.64 [95% confidence interval (95% CI): 1.23-2.18). The difference was most prominent when small early trials published in HIG journals were compared with subsequent trials [sROR 2.68 (95% CI: 1.33-5.38)]. Late-published HIG trials showed no consistent inflation of effects. The patterns did not differ beyond chance between NEJM, JAMA or Lancet.


Small trials published in the most prestigious journals show more favourable effects for experimental interventions, and this is most prominent for early-published trials in such journals. No effect inflation is seen for large trials.

[PubMed - indexed for MEDLINE]
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