Unfavourable results from clinical trials often go unpublished

Trials showing a positive treatment effect, or those with important or striking findings, are much more likely to be published in scientific journals than those with negative findings, a new review from The Cochrane Library has found. 

‘This publication bias has important implications for healthcare. Unless both positive and negative findings from clinical trials are made available, it is impossible to make a fair assessment,’ said Sally Hopewell of the Cochrane Centre.

The international team of researchers carried out a systematic review of all the existing research in this area. In addition to showing that negative results were published less often, they found that if these results were eventually published, they would take between one and four more years to appear in journals than studies showing positive results.

Results from one of the five studies in the review indicated that investigators and not editors might be to blame. The reasons most commonly given for not publishing were that investigators thought their findings were not interesting enough or they did not have time.

‘The registration of all clinical trial protocols before they start should make it easier to identify where we are missing results,’ commented Kay Dickersin from Johns Hopkins University in Baltimore, USA, another of the researchers on this project.

The Cochrane researchers say their study also highlights the need for a world-wide commitment to the disclosure of the findings of clinical trials.

Mike Clarke of Trinity College Dublin stated: ‘The World Health Organization recently found widespread support for the development of such a process.’