Trials showing a positive treatment effect, or those with important or striking findings, were 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 of a drug's safety and efficacy," says lead researcher, Sally Hopewell of the UK Cochrane Centre in Oxford, UK.
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 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," says Kay Dickersin from Johns Hopkins University in Baltimore, USA, another of the researchers on this project.
One of the other researchers, Kirsty Loudon, based in Scotland, adds, "Registration of trials and their results would help people conducting systematic reviews to look at both published and unpublished evidence, to reach reliable conclusions."
The researchers say their study also highlights the need for a worldwide commitment to the disclosure of the findings of clinical trials. Mike Clarke of Trinity College Dublin in Ireland, says, "The World Health Organisation recently found widespread support for the development of such a process."
Andy Oxman from the Norwegian Knowledge Centre for Health Services concludes, "Healthcare decisions need to be based on all the evidence, not just the most exciting results."
- Hopewell S, Loudon K, Clarke MJ, Oxman AD, Dickersin K. Publication bias in clinical trials due to statistical significance or direction of trial results. Cochrane Database of Systematic Reviews, Issue 1. Art. No.: MR000006 DOI: 0.1002/14651858.MR000006.pub3
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