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.

The authors compared the information available in clinical study reports and in publicly accessible sources (journal articles, registry reports) included in 16 HTA reports for drugs prepared in IQWiG. They assessed the completeness of information on patient-relevant benefit (e.g. symptom relief, health related quality of life) and harm (adverse effects) outcomes reported in each document type. Clinical study reports provided complete information of all outcomes on a higher proportion (86%) than publicly accessible sources (39%). They also provided more information on harms (87% versus 43 %). The authors conclude that clinical study reports should be made publicly available for the benefit of unbiased trial evaluation and informed decision-making in health care.