Cochrane Central Register of Controlled Trials

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”

Reviewer(s): 
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 ClinicalTrials.gov 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 This study aimed to investigate whether searching CENTRAL alone was sufficient for identifying ongoing and unpublished studies.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 ClinicalTrials.gov or ICTRP. 16 of these studies were not indexed in CENTRAL.

The authors conclude that ClinicalTrials.gov 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 ClinicalTrials.gov. 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
Related Chapters: 

Appraisal of: Craven J, Jefferies J, Kendrick J, Nicholls D, Boynton J, Frankish R. A comparison of searching the Cochrane library databases via CRD, Ovid and Wiley: implications for systematic searching and information services. Health Info Libr J. 2014

Reviewer(s): 
Short description: 

The different interfaces for searching Cochrane Library databases are compared in this paper. Firstly CENTRAL and CDSR are compared via Ovid and Wiley and then DARE, NHS EED and HTA databases are compared via Ovid, Wiley and the CRD website. The authors explore search syntax comparisons including proximity operators, MeSH headings, search term order and fields searched. The authors found that there were differences in the use of MeSH headings, searching for free text and using proximity operators. They also suggest a “best match” search syntax to be used across the different interfaces. 

Limitations stated by the author(s): 

Firstly only certain aspects of interface functionality were examined and compared. Secondly only a small number of terms were used to explore each of the search functions. Thirdly the relevance or usefulness of additional records found via one interface but not another was not explored. Lastly, each difference in search syntax was examined individually and not in a combination of search terms/ search string as would happen in the real world.

A follow-up study is planned: to apply the findings to more real-life by comparing full search strategies.

Limitations stated by the reviewer(s): 
The demise of DARE and NHS EED will impact on the relevance of this paper. Cannot find any numbers on how many unique references there were in the different interfaces. No analysis on recall and precision.
Study Type: 
Single study
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