Completed clinical studies registered on the US-based ClinicalTrials.gov database and subsequently published in the biomedical literature took a median of 21 months to be published in 2009, a new study has found.

A research team led by Dr Joseph Ross from Yale University School of Medicine in the US analysed clinical trials published during the 2009 calendar year that were cited in the US National Library of Medicine's bibliographic database, MEDLINE, and linked to a ClinicalTrials.gov identifier.

As Ross et al noted in a Research Letter to the Journal of the American Medical Association publication JAMA Internal Medicine, previous studies (including one published last year by Ross and colleagues in the BMJ) have shown that between 25% and 50% of clinical trials are never published.

However, “among those published, we know little about the length of time required for publication in the peer-reviewed biomedical literature after study completion”, they added.

The BMJ analysis by Ross et al found that the average time to publication of studies funded primarily or partially by the US National Institutes of Health and registered on ClinicalTrials.gov was 23 months.

Qualifying trials

In the latest analysis, Ross and his colleagues looked at 1,336 qualifying trials published during calendar 2009, the majority of which (719 or 54%) were funded by non-profit organisations. Industry accounted for a further 32% and government for 14%. The bulk of the trials (95%) were interventional and the rest observational.

The interquartile range for the median publication time of 21 months was 13 to 32 months, while there were only modest differences across trials types.

In terms of funding sources, industry-backed trials took longer (a median of 24 months) to publish than studies funded by non-profits (20 months) or government (20 months).

The median time to publication for Phase I trials was 20 months, while it was 19 months for Phase I/II or Phase II studies, 22 months for Phase II/II or III and 20 months for Phase IV.

The researchers acknowledged that study findings may have been disseminated by means other than publication, such as presentations at scientific meetings. However, “with the exception of public results reporting, these alternative demonstration strategies lead to limited public awareness of the research”, they observed.

“Given the time required to publish results from these clinical trials, our findings support current federal initiatives requiring results reporting of clinical studies within 12 months of trial completion to ensure the timely dissemination of clinical science,” Ross et al concluded.