Using the Cochrane Central Register of Controlled Trials to identify clinical trial registration is insufficient: a cross-sectional study

Abstract

Background: While conducting systemic reviews, searching for ongoing or unpublished trials is critical to address publication bias. As of April 2019, records of ongoing or unpublished randomized and/or quasi-randomized controlled trials registered in the International Clinical Trials Registry Platform (ICTRP) and ClinicalTrials.gov are available in the Cochrane Central Register of Controlled Trials (CENTRAL). These records registered in CENTRAL include studies published since the inception of ICTRP and ClinicalTrials.gov. Whether systematic reviewers can search CENTRAL to identify ongoing or unpublished trials instead of ICTRP and ClinicalTrials.gov is unknown. Methods: This was a cross-sectional study. A consecutive sample of ongoing or unpublished studies published from June 1, 2019 to December 27, 2019 was selected from the Cochrane Reviews. The sensitivity and the number needed to read (NNR) were assessed from among the studies selected from CENT RAL instead of ICTRP and ClinicalTrials.gov and also assessed the characteristics of studies not identified by searching CENTRAL. Results: In total, 247 records from 50 Cochrane reviews were included; of these, 200 were identified by searching CENTRAL, whereas the remaining 47 records were not. The sensitivity of searching CENTRAL was 0.81 (95% confidence interval [CI]: 0.76, 0.85). The NNR was 115 (95% CI: 101, 133). The 47 unidentified studies were registered through ClinicalTrials.gov or ICTRP. Sixteen unidentified studies were not indexed in CENTRAL. Conclusions: For systematic reviewers, searching CENTRAL could not substitute for searching ClinicalTrials.gov and/ or ICTRP. Systematic reviewers should not only search CENTRAL but also ICTRP and ClinicalTrials.gov to identify unpublished trials.

How do search systems impact systematic searching? A qualitative study

“…These prior studies described the challenges of grey literature retrieval, improvement to which is perhaps the most urgent priority revealed in the interviews. While the Cochrane Central Register of Controlled Trials (CENTRAL) provides access to trials data with better search and export functionality, it is not comprehensive enough to be the only means of identifying unpublished trials [ 30 ]. There is a clear demand for grey literature search systems that better meet the needs of systematic searchers.…”

A technical review of three clinical trials register resources indicates where improvements to the search interfaces are needed

“…CENTRAL); or more simply by exporting ICTRP records to Excel to search as opposed to searching via the ICTRP interface. Evaluation studies which compared the effectiveness and efficiency of study identification using these methods would represent a valuable contribution to information retrieval research 50,53 …”

“…Evaluation studies which compared the effectiveness and efficiency of study identification using these methods would represent a valuable contribution to information retrieval research. 50,53 We repeat the call for increased and joined-up dialogue between the people who provide trials register resources (and maintain/develop their interfaces) and their users. 43 Thinking through how people use these resources and the data within them might benefit both groups.…”

The Meta-Analysis in Evidence-Based Medicine: High-Quality Research When Properly Performed

“…To minimize bias associated with narrow collection of sources and usage of only the most popular databases, one needs to broaden the scope of databases used. This includes electronic sources such as Cochrane Central, 14 the Federal Drug Administration, and internet websites such as Google scholar. Examples of search strategies can be found in the Cochrane Collaboration's Reviewers' handbook.…”