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© 2018 Fleminger, Goldacre. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Objective Trial registries are a key source of information for clinicians and researchers. While building OpenTrials, an open database of public trial information, we identified errors and omissions in registries, including discrepancies between descriptions of the same trial in different registries. We set out to ascertain the prevalence of discrepancies in trial completion status using a cohort of trials registered on both the European Union Clinical Trials Register (EUCTR) and Study design and setting We used matching titles and registry IDs provided by both registries to build a cohort of dualregistered trials. Completion statuses were compared; we calculated descriptive statistics on the prevalence of discrepancies. Results 11, 988 dual-registered trials were identified. 1, 496 did not provide a comparable completion status, leaving 10, 492 trials. 16.2% were discrepant on completion status. The majority of discrepancies (90.5%) were a 'completed' trial on inaccurately marked as 'ongoing' on EUCTR. Overall, 33.9% of dual-registered trials described as 'ongoing' on EUCTR were listed as 'completed' on Conclusion Completion status on registries is commonly inaccurate. Previous work on publication bias may underestimate non-reporting. We describe simple steps registry owners and trialists could take to improve accuracy.

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