Objective: To compare the recent trends and characteristics of studies registered as non-ClinicalTrials.gov in the International Clinical Trials Registry Platform (ICTRP).
Study design and setting: We included all studies on the ICTRP from January 1, 2014, to December 31, 2018. We described the characteristics of included studies and examined whether the proportion of studies registered in non-ClinicalTrials.gov on ICTRP increased by interventional design or noninterventional design. We further compared the characteristics of studies registered in non-ClinicalTrials.gov to those registered in ClinicalTrials.gov.
Results: We identified 235,830 studies (182,771 studies having interventional design and 53,059 studies having noninterventional design). The proportion of studies registered in non-ClinicalTrials.gov among studies registered on ICTRP increased from 2014 to 2018 (38.3% to 53.3% overall, 39.3% to 53.0% for interventional design, and 34.1% to 54.2% for noninterventional design). Studies registered in non-ClinicalTrials.gov were more often retrospectively registered as interventional design and lacked sufficient information about target sample sizes than studies registered in ClinicalTrials.gov irrespective of study design.
Conclusion: Studies registered in non-ClinicalTrials.gov increasingly accounted for the proportion of protocol registration among the ICTRP irrespective of study designs since 2014. Systematic reviewers should search ICTRP in addition to ClinicalTrials.gov.
Keywords: Clinical trials registry; ClinicalTrials.gov; International Clinical Trials Registry Platform; Meta-Research; Protocol registration.
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