Clinical trials are published, on average, almost two years after completion, with time to publication affected by the funding source, number of trial participants, and journal impact factor, according to a research letter published online in JAMA Internal Medicine.

Joseph S. Ross, MD, MHS, from the Yale University School of Medicine in New Haven, Conn., examined the time to publication for a representative sample of clinical trials published in 2009, identified via

During the 2009 calendar year, the researchers found 1,336 trials published that were indexed via MEDLINE and linked to a identifier. Most had more than 100 participants enrolled and were funded by nonprofit organizations. The median time to publication was 21 months (interquartile range, 13 to 32 months). Among trials funded by industry the time to publication was longer than for government- or nonprofit organization-funded trials (24 vs. 20 months). There was a shorter time to publication for trials involving 1,000 or more participants than for those with 100 or fewer participants or 100 to 1,000 participants (18, 20, and 23 months, respectively). The journal impact factor affected time to publication, which was shorter for trials published in journals with an impact factor greater than 10 versus less than 10 (17 vs. 23 months).

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“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,” the authors write.