Attribution of non-ClinicalTrials.gov registries among WHO International Clinical Trials Registry Platform-registered trials from 2014 to 2018: A protocol for a meta-epidemiological study

Background. The attribution of non-ClinicalTrials.gov registries among registered trials of the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) had increased until 2013. However, the attribution after 2013 is unknown. Moreover, no study has investigated the usage of non-ClinicalTrials.gov registries after 2015 or compared the characteristics of trials under non-ClinicalTrials.gov and ClinicalTrials.gov registries. Methods. This will be a meta-epidemiological study. It will include all trials registered on the ICTRP from January 1, 2014, to December 31, 2018. First, we will describe the total attribution of non-ClinicalTrials.gov registries among the ICTRP-registered trials for each year and each registry worldwide. Second, we will compare the recruitment status, target sample size, study type, study design, countries, prospective registration, funding, and study phase of the trials on ClinicalTrials.gov and other registries from 2014 to 2018. Third, we will report on the distribution of primary registries of trials from the top five countries in order of the quantity of registered trials on the ICTRP. Ethics & Dissemination. Ethics approval is not required for this study. This protocol has been registered in the University Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR). The findings will be published in a peer-reviewed journal and may be presented at conferences. Trial Registration Number. UMIN000034401