Introduction: Clinical trial registries that include prospective registration of study protocols and summarized results can inform the prevalence and impact of information bias. This methods report examines the feasibility and added utility of comprehensive searches of registries to supplement the evidence identified in an ongoing systematic review update on omega-3 fatty acids (n-3 FA) and CVD outcomes.
Data sources: We conducted searches in ClinicalTrials.gov and the International Clinical Trials Registry Platform, using terms that matched those used in the original review database searches.
Results: The original report included 98 studies (61 randomized controlled trials in 82 articles, and 37 longitudinal observational studies in 65 articles). We compared our registry search yield with our original report to identify studies: (1) registry record present, included in original review (26 studies, 4 with eligible results); we found that, in general, the agreement between the registry record and the published paper was good when the information was given in both. (2) Registry record present, not included in original review (43 studies); of these 23 were completed, 10 were ongoing, and 13 had unknown status. A single record yielded a new publication emanating from a study included in the original report. (3) No registry record, included in original review (72 studies); we posit that this is, in part, because many of the studies in the report predate the requirement to register trials.
Conclusions: While we found that for this project, searching registry data added little to the evidence, one way in which conducting a registry search is of value to a systematic review project is in identifying ongoing research and gaps in knowledge. Several of the studies not found in the original review but identified through registry searches were unfinished or in progress at the time of the search. These studies should be taken in to account when evaluating the state of the literature and calling for future research.