Now that CENTRAL indexes clinical trials registry records, should I still search ClinicalTrials.gov?
Cochrane Central Register of Controlled Trials (CENTRAL) is an ongoing dream for systematic reviewers interested in finding all randomised controlled trials (RCTs) in one place. A one-stop-shop. As part of the efforts to be as inclusive as possible, CENTRAL started including records of randomised controlled trials (RCTs) from other sources such as MEDLINE, Embase, KoreaMed, CINAHL, ClinicalTrials.gov, and WHO ICTRP (World Health Organisation’s International Clinical Trials Registry Portal). Leave alone that the negotiation team must have done a brilliant job convincing the publishers/owners to contribute to CENTRAL, the outcome is not always what we expect.
The question if CENTRAL is enough has been brought out within the Cochrane Information Specialists’ community at least three times (1, 2, 3), and each time, we hesitate to replace ClinicalTrials.gov with CENTRAL.
Here I summarise why searching CENTRAL and ClinicalTrials.gov are very different and what to consider before making your final decision on searching CENTRAL or CENTRAL plus ClinicalTrials.gov.
1. Differences in Search Fields in ClinicalTrials.gov and CENTRAL
A classic bibliographic database has bibliographic or reference records with fields such as title, abstract, authors, publication year, journal name, volume, DOI, and page numbers. As a result, you can run searches in these fields.
Clinical trial registries contain study records, not reference records. As a result, you can search Healthcare Condition, Population, Interventions, Outcomes, Registration Date, Completion Date, and so on. Such study records may also contain the title, DOI, and summary. You can imagine how this will affect the search strategy:
If you search ClinicalTrials.gov directly, you will search Healthcare Condition and Interventions; however, if you search its content as indexed in CENTRAL, you will search title, abstract, and keywords.