Abstract
BackgroundTo increase transparency in research, the International Committee of Medical Journal Editors required, in 2005, prospective registration of clinical trials as a condition to publication. However, many trials remain unregistered or retrospectively registered. We aimed to assess the association between trial prospective registration and treatment effect estimates.MethodsThis is a meta-epidemiological study based on all Cochrane reviews published between March 2011 and September 2014 with meta-analyses of a binary outcome including three or more randomised controlled trials published after 2006. We extracted trial general characteristics and results from the Cochrane reviews. For each trial, we searched for registration in the report’s full text, contacted the corresponding author if not reported and searched ClinicalTrials.gov and the International Clinical Trials Registry Platform in case of no response. We classified each trial as prospectively registered (i.e. registered before the start date); retrospectively registered, distinguishing trials registered before and after the primary completion date; and not registered. Treatment effect estimates of prospectively registered and other trials were compared by the ratio of odds ratio (ROR) (ROR <1 indicates larger effects in trials not prospectively registered).ResultsWe identified 67 meta-analyses (322 trials). Overall, 225/322 trials (70 %) were registered, 74 (33 %) prospectively and 142 (63 %) retrospectively; 88 were registered before the primary completion date and 54 after. Unregistered or retrospectively registered trials tended to show larger treatment effect estimates than prospectively registered trials (combined ROR = 0.81, 95 % CI 0.65–1.02, based on 32 contributing meta-analyses). Trials unregistered or registered after the primary completion date tended to show larger treatment effect estimates than those registered before this date (combined ROR = 0.84, 95 % CI 0.71–1.01, based on 43 contributing meta-analyses).ConclusionsLack of trial prospective registration may be associated with larger treatment effect estimates.Electronic supplementary materialThe online version of this article (doi:10.1186/s12916-016-0639-x) contains supplementary material, which is available to authorized users.
Highlights
To increase transparency in research, the International Committee of Medical Journal Editors required, in 2005, prospective registration of clinical trials as a condition to publication
We aimed to investigate whether there is a difference in treatment effect estimates according to trial prospective registration
According to the Cochrane handbook, the blinding and incomplete outcome data domains should be assessed at the outcome level; for reviews reporting an evaluation of these domains by outcome or type of outcome, we manually identified the outcome corresponding to the selected meta-analysis
Summary
To increase transparency in research, the International Committee of Medical Journal Editors required, in 2005, prospective registration of clinical trials as a condition to publication. We aimed to assess the association between trial prospective registration and treatment effect estimates. In 2005, the International Committee of Medical Journal Editors (ICMJE) initiated a policy for trial registration to increase transparency in research. Dechartres et al BMC Medicine (2016) 14:100 Another found that 39 % of published trials retrieved from MEDLINE appeared not to have been registered [6]. Some researchers generated an important debate among the medical community, arguing that trials published after 2010 that are not prospectively registered should be excluded from Cochrane reviews [7]. The evidence is as yet unclear concerning a possible association between trial registration and treatment effect estimates [14]
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