Non-publication of clinical trial results was common and the availability of results in in a government-funded database was limited, with higher non-publication rates among industry-funded trials, an analysis found.
To estimate the frequency with which results of large randomized clinical trials registered with ClinicalTrials.gov are not available to the public, researchers conducted a cross sectional analysis of trials with at least 500 participants that were prospectively registered with ClinicalTrials.gov and completed prior to January 2009. The final literature search occurred in November 2012.
Results appeared online Oct. 29 at BMJ.
Of 585 registered trials, 171 (29%) remained unpublished. Among trials with a completion date listed in ClinicalTrials.gov (n=542) and that had been published (389/542, 72%), the median time from study completion to publication was 27 months (interquartile range 20-37 months).
Of the 171 trials that remained unpublished, 38 (22%) had results available on ClinicalTrials.gov. Among all 585 trials, 414 (71%) had published results, 38 (6%) were unpublished but had results available on ClinicalTrials.gov, and 133 (23%) had no results available either in either medium.
Fifteen (39%) of the 38 trials with results reported also provided statistical analyses for at least 1 primary outcome. Nine of these 15 (60%) reported statistically significant results clearly favoring the intervention, whereas another four (27%) reported meeting a standard of non-inferiority. The other 23 trials that were unpublished but had results available on ClinicalTrials.gov reported results without statistical analyses. Of 38 trials with results provided, 37 (97%) included safety endpoints or adverse events.
Non-publication was more common among trials that received industry funding (150/468, 32%) than those that did not (21/117, 18%; P=0.003). Of the 171 unpublished trials, 133 (78%) had no results available in ClinicalTrials.gov.
Researchers noted that nearly 300,000 study participants were exposed to the risks of being in a medical study, but without societal benefits that come from reporting trial results. They described publishing trial results as an ethical obligation.
“Even when study investigators and sponsors make their results available in ClinicalTrials.gov, this should not absolve them from their obligation to publish data in a peer reviewed format,” the authors wrote. Peer review can identify study bias, ensure statistical rigor, places study results into context, and facilitates access by the rest of the scientific community.
“While the ability of ClinicalTrials.gov to display results is an important step forward, this capability is not a substitute for the peer review process,” they concluded.