OBJECTIVE

PROSPERO, an international prospective register of systematic reviews, was launched in February 2011 to reduce publication bias of systematic reviews (SRs). A questionnaire survey of SR researchers conducted in 2005 indicated the existence of unpublished SRs and the potential influence of lack of funding as a reason for non-publication. Here, we investigated the publication status of registered SRs in the 1st year that PROSPERO launched and assessed the association between publication and the existence of funding or conflicts of interest (COIs).

RESULTS

We identified 326 SRs registered in PROSPERO from February 2011 through February 2012. Among them, 85 SRs (26%) remained unpublished at least 65 months after registration. We found 241 published reports, including four conference abstracts and one poster presentation. Median time to publication from protocol registration was 16.3 months. Funding for SRs was associated with publication [odds ratio (OR) = 2.10; 95% confidence interval (CI) = 1.26 to 3.50]. We found no significant association of author-reported COIs with publication (OR = 2.35; 95% CI = 0.67 to 8.20). Twenty SRs were not published despite the authors reporting completion of the reviews in PROSPERO.