Time to publication for results of clinical trials (Cochrane Methodology Review)

It has been suggested that a time-lag bias exists whereby research studies with striking results are more likely to be stopped earlier than originally planned, published quicker or both. If time-lag bias exists, such that the results of studies with positive findings become available sooner than those with null or negative findings, new interventions might be mistakenly assumed to be effective in the absence of evidence to the contrary.

To systematically review studies that have investigated the possibility of time-lag bias and to determine the extent to which the time to publication of a clinical trial is influenced by the significance of its result.

Studies were identified by searching the Cochrane Methodology Register, MEDLINE, EMBASE, Science Citation Index and by handsearching journals and conference abstracts. The date of the most recent search was March 2001.

A study was considered eligible for this review if it contained analyses of any aspect of the time to publication of clinical trials and tracked the publication of a cohort of clinical trials.

Data extraction was performed independently by two reviewers. Data were extracted on the median time from the date the trial started to the date of publication of its results. Data were also extracted on the methodological quality of the included research study, the source of the clinical trials under investigation, the source of funding, the area of health care, the means by which the publication status of these trials were sought, and the rate of publication.

Two studies met the inclusion criteria. In both studies just over half of all trials had been published in full. Trials with positive results (i.e. those with statistically significant results (p<0.05) in favour the experimental arm of the trial) tended to be published in approximately 4 to 5 years. This was quicker than for those with null or negative results (i.e. those with results that were not statistically significant (p=>0.05) or statistically significant (p<0.05) in favour of the control arm of the trial) with a time to publication of around 6 to 8 years. One of the studies suggests that this difference could, in part, be attributed to the length of time taken to publish the results of a trial once follow up has been completed. This study showed that trials with null or negative findings took, on average, just over a year longer to be published than those with positive results.

Authors' conclusions:

Our review confirms that trials with positive results are published sooner than those with null or negative results. This has important implications for the timing of the initiation and updating of a review, especially if there is an association between the inclusion of a trial in a review and its publication status. It is of particular concern when one considers reviews in which only a small number of studies have been published and are available for the review.

Citation: Hopewell S, Clarke M, Stewart L, Tierney J.. Time to publication for results of clinical trials (Cochrane Methodology Review). The Cochrane Database of Methodology Reviews 0000, Issue . Art. No.: MR000011. DOI:10.1002/14651858.MR000011.