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Trial results and publication bias

Post compliments of Anne Taylor-Vaisey:

Publication bias resulting from the publishing of only positive results of trials has been well documented, and has resulted in the recent publication of the following statement in the major medical journals:

Clinical trial registration: a statement from the International Committee of Medical Journal Editors [ICMJE]. CMAJ 2004 Sep 14;171(6):606-7.

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The ICMJE member journals will require, as a condition of consideration for publication, registration in a public trials registry. Trials must register at or before the onset of patient enrollment. This policy applies to any clinical trial starting enrollment after July 1, 2005. For trials that began enrollment before ! this date, the ICMJE member journals will require registration by Sept. 13, 2005, before considering the trial for publication.

The current issue of CMAJ includes the following study about outcome reporting bias in CIHR funded trials:

Outcome reporting bias in randomized trials funded by the Canadian Institutes of Health Research. CMAJ " September 28, 2004; 171 (7). doi:10.1503/cmaj.1041086. An-Wen Chan, Karmela Krlea-Jeri, Isabelle Schmid and Douglas G. Alt.

Background: The reporting of outcomes within published randomized trials has previously been shown to be incomplete, biased and inconsistent with study protocols. We sought to determine whether outcome reporting bias would be present in a cohort of government-funded trials subjected to rigorous peer review.

Methods: We compared protocols for randomized trials approved for funding by the Canadian Institutes of Health Research (formerly the Medical Research Council of Canada) from 1990 to 1998 with subsequent reports of the trials identified in journal publications. Characteristics of reported and unreported outcomes were recorded from the protocols and publications. Incompletely reported outcomes were defined as those with insufficient data provided in publications for inclusion in meta-analyses. An overall odds ratio measuring the association between completeness of reporting and statistical significance was calculated stratified by trial. Finally, primary outcomes specified in trial protocols were compared with those reported in publications.

Results: We identified 48 trials with 68 publications and 1402 outcomes. The median number of participants per trial was 299, and 44% of the trials were published in general medical journals. ! A median of 31% (10th 90th percentile range 5% 67%) of outcomes measured to assess the efficacy of an intervention (efficacy outcomes) and 59% (0% 100%) of those measured to assess the harm of an intervention (harm outcomes) per trial were incompletely reported. Statistically significant efficacy outcomes had a higher odds than nonsignificant efficacy outcomes of being fully reported (odds ratio 2.7; 95% confidence interval 1.5 5.0). Primary outcomes differed between protocols and publications for 40% of the trials.

Interpretation: Selective reporting of outcomes frequently occurs in publications of high-quality government-funded trials.

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