Reducing publication bias through trial registration.

Publication bias is the systematic, preferential publication of studies with statistically significant positive results over indeterminate studies (frequently, researchers inappropriately term these "negative" studies), or studies that show a statistically significant negative outcome. Over time, this practice distorts the medical literature, potentially compromising the validity of systematic reviews. Publication bias primarily stems from investigators, but data suppression can occur by pharmaceutical companies, universities, and regulatory agencies. Registration at inception of all clinical trials in a centralized, searchable database can reduce publication bias by enabling researchers to identify all studies related to a particular intervention. Prior attempts to encourage voluntary trial registration have been largely unsuccessful. Hence, the International Committee of Medical Journal Editors recently adopted a policy of mandatory clinical trial registration before consideration of manuscripts for publication. Trial registration and the development of comprehensive, computerized databases will promote transparency in research and help reduce publication bias.