Appraisal of: “Banno M, Tsujimoto Y, Kataoka Y. Using the Cochrane Central Register of Controlled Trials to identify clinical trial registration Is insufficient: a cross-sectional study. BMC Med Res Methodol. 2020, 20: 200”

Short description: 

The CENTRAL (Cochrane Central Register of Controlled Trials) database (available via The Cochrane Library) is a source of randomized and quasi-randomized controlled trials. CENTRAL is populated from multiple database sources, including clinical trial registries such as and ICTRP. This study aimed to investigate whether searching CENTRAL alone was sufficient for identifying ongoing and unpublished studies.

The authors created a set of clinical trials registrations included in a sample of 50 Cochrane reviews published in 2019. The authors tested whether the search strategies for CENTRAL documented in these reviews would retrieve all the included clinical trial registrations.

Searches of CENTRAL database with the documented Cochrane review search strategies identified only 200 of the 247 clinical trial registrations. All 47 of the unidentified studies were registered in either or ICTRP. 16 of these studies were not indexed in CENTRAL.

The authors conclude that and ICTRP should be searched in addition to CENTRAL.

Limitations stated by the author(s): 

The authors describe the following limitations of this study:

  • the focus was on Cochrane systematic reviews only, and findings may not be generalisable to non-Cochrane reviews
  • CENTRAL only includes controlled trials so the findings cannot be applied to systematic reviews of observational studies.
  • There was variation in the search strategies used for CENTRAL, ICTRP and However, the authors suggest CENTRAL search strategies were unlikely to be of low quality, as these were mostly developed by Information Specialists with extensive search expertise.
Limitations stated by the reviewer(s): 
No additional limitations detected by the reviewers.
Study Type: 
Single study
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