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 ClinicalTrials.gov.

Study Design and Setting

We used matching titles and registry IDs provided by both registries to build a cohort of dual-registered trials. Completion statuses were compared; we calculated descriptive statistics on the prevalence of discrepancies.


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 ClinicalTrials.gov inaccurately marked as ‘ongoing’ on EUCTR. Overall, 33.9% of dual-registered trials described as ‘ongoing’ on EUCTR were listed as ‘completed’ on ClinicalTrials.gov.


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.