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Around a third of clinical trials are not published

29% of trials not published after five years

Adrian O'Dowd

Wednesday, 30 October 2013

Around a third of large clinical trials are not published five years after they have been completed, according to a study published online today by the BMJ.

US researchers also found that of those unpublished trials, 78% had no results publicly available, meaning that an estimated 250,000 people had been exposed to the risks of trial participation without any societal benefits from publicising the results.

Randomised clinical trials are an important way of advancing medical knowledge and are dependant on the willingness of people to expose themselves to risks. Most do so because of the likelihood that these risks will benefit society in general from knowledge gained from the trial.

In the US, law requires that many trials involving human participants are registered and their results posted on the largest clinical trial website ClinicalTrials.gov.

However, there are concerns that this legislation if sometimes ignored so a team of US-based researchers set out to estimate the frequency of non-publication of trial results and, among unpublished studies, the frequency with which results were unavailable in the ClinicalTrials.gov database.

The researchers, led by Dr Christopher Jones, attending physician in the Department of Emergency Medicine, Cooper Medical School of Rowan University, New Jersey, and colleagues from the University of North Carolina identified 585 trials with at least 500 participants that were registered with ClinicalTrials.gov and completed before to January 2009.

The average time between study completion and the final literature search (November 2012) was 60 months for unpublished trials.

They then reviewed registry entries for unpublished trials to determine whether results for these studies were available in the ClinicalTrials.gov results database.

Of the 585 registered trials, 171 (29%) remained unpublished. Of these, 133 (78%) had no results available in ClinicalTrials.gov.

They researchers also found that non-publication was more common among trials that received industry funding (32%) than those that did not (18%) receive such funding.

The authors said: “Our results add to existing work by showing that non-publication is an important problem even among large randomised trials.

“The lack of availability of results from these trials contributes to publication bias and also constitutes a failure to honor the ethical contract that is the basis for exposing study participants to the risks inherent in trial participation.

“Additional safeguards are needed to ensure timely public dissemination of trial data.”

DOI: http://dx.doi.org/10.1136/bmj.f6104

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