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10.3.3  Trial registries and publication bias

In September 2004 a number of major medical journals belonging to the International Committee of Medical Journal Editors (ICMJE) announced they would no longer publish trials that were not registered at inception (Abbasi 2004). All trials that began enrolment of participants after September 2005 had to be registered in a public trials registry at or before the onset of enrolment to be considered for publication in those journals. The ICMJE described ‘acceptable’ registers: electronically searchable, freely accessible to the public, open to all registrants, and managed by a non-profit organization. Similarly, the ICMJE asks clinical trialists to adhere to a minimum dataset proposed by the World Health Organization.


If this long-overdue initiative is successful, it has the potential to substantially reduce the effects of publication bias. However this would depend on review authors identifying all relevant trials by searching online trial registries, and also on the results of unpublished trials identified via registries being made available to them. Initiatives to mandate the registration of trial results are currently in the early stages, are evolving quickly, and should have an impact on the accessibility of these data.  While there is emerging evidence suggesting that some of the data fields requested in the registries are incomplete (Zarin 2005), this is likely to improve over time. The extent to which trial registration will facilitate the work of Cochrane review authors is unclear at present. For advice on searching trial registries, see Chapter 6 (Section 6.2.3).