Background: We have updated and combined two Cochrane methodology reviews, “Time to publication for results of clinical trials” (searches done in 2005) and “Publication bias in clinical trials due to statistical significance or direction of trial results” (2007). Since their publication, the much greater use of trial registries has allowed researchers to study publication bias in greater depth. We now summarise and present the up-to-date picture with regard to publication bias. This topic is relevant and important to clinicians and patients as nonpublished evidence is wasted evidence.
Objectives: To determine publication rate and time to publication of clinical trials.
Methods: We searched MEDLINE, Embase, Epistemonikos and the Cochrane Methodology Register from 2005 to 29 April 2021 for reports analysing any aspect of the publication rate or time to publication for clinical trials. We excluded reports that solely examined cohorts of published papers or solely used results made available on registry portals as evidence of publication. Two authors independently screened all studies, read full texts and completed risk of bias assessments and data extraction. The following outcomes were collected: Primary: (1) proportion of studies that are published and (2) time to publication of published studies; Secondary: relationships between positive results, sample size, multicentre and type of funding and publication and time to publication. Results and
Conclusions: The original Cochrane Methodology Reviews included a total of five studies (published between 1992 and 1998). We have added a further 156 studies with this update. We will present results from the 161 studies now included in this review and discuss the implications for those using clinical trials to make decisions about health and social care.

Figure 1 for Colloquium abstract.pdf