University of Ioannina Finds a Great Number of Large Trials Not Publishing Results


University of Ioannina School of Health Sciences researchers found that a significant amount of large clinical studies are not reported, which could “threaten the credibility” of published clinical research evidence, according to the study which was published in the Annals of Internal Medicine.

The researchers studied from 2007 to 2012 and thereafter identified the 500 studies with the largest participant enrollment that were unpublished had no results posted as of April 22, 2016.


  • The investigators precluded trials that were nonrandomized, cluster-randomized and non-preregistered
  • The researchers identified 146 large randomized controlled trial with no results published
    • They ultimately narrowed the number down to 70
  • 67 long-unreported trials, there were 87,8823 participants involved
  • Average median enrollment 765 participants and went unreported a median of 9 years after completion

Summary: A significant number of large clinical trials go unreported.

Lead Research/Investigator

Athina Tatsioni, MD, University of Ionnina