Appraisal of: Banno, M et al (2019) Studies registered in non-ClinicalTrials.gov accounted for an increasing proportion of protocol registrations in medical research. J Clin Epidemiol 2019;116:106.

Reviewer(s): 
Short description: 

The objective of the study was to identify the proportion of registered studies in WHO ICTRP not included in ClinicalTrials.gov (described as non-ClinicalTrials.gov studies). The study also compares the characteristics of studies identified as non-ClinicalTrials.gov with those registered in ClinicalTrials.gov.

A total of 235,830 studies were identified as being on the ICTRP website between 2014-2018. The proportion of studies registered as non-ClinicalTrials.gov increased during that time from 38.3% to 53.3%. The proportion of non-ClinicalTrials.gov studies with a randomised design (among all studies with a randomised design registered on ICTRP) increased during that time from 43.9% to 56.7%. Non-ClinicalTrials.gov studies were more often retrospectively registered and lacked key information. Systematic review searches should include a search of ICTRP in addition to ClinicalTrials.gov.

Limitations stated by the author(s): 

The data included only studies registered in the ICTRP, other sources were not examined. The post hoc sensitivity analysis restricting to randomised controlled trials might be misclassified due to the keywords used.

Limitations stated by the reviewer(s): 
No additional limitations detected by the reviewers.
Study Type: 
Single study