Outcome reporting bias in randomized trials funded by the Canadian Institutes of Health Research

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.Selective reporting of results from randomized trials can occur either at the level of end points within published studies (outcome reporting bias)¹ or at the level of entire trials that are selectively published (study publication bias).² Outcome reporting bias has previously been demonstrated in a broad cohort of published trials approved by a regional ethics committee.¹ The Canadian Institutes of Health Research (CIHR) — the primary federal funding agency, known before 2000 as the Medical Research Council of Canada (MRC) — recognized the need to address this issue and conducted an internal review process in 2002 to evaluate the reporting of results from its funded trials. The primary objectives were to determine (a) the prevalence of incomplete outcome reporting in journal publications of randomized trials; (b) the degree of association between adequate outcome reporting and statistical significance; and (c) the consistency between primary outcomes specified in trial protocols and those specified in subsequent journal publications.