Both clinical trial register and electronic bibliographic database searches were needed to identify randomized clinical trials for systematic reviews: an evaluation study

Tabea Kaul, Julia M. T. Colombijn, Robin W. M. Vernooij, Rene Spijker, Demy L. Idema, Linde F. Huis in ‘t Veld, Johanna A. A. Damen, Lotty Hooft

Research output: Contribution to journalArticleAcademicpeer-review


Objectives: To determine whether clinical trial register (CTR) searches can accurately identify a greater number of completed randomized clinical trials (RCTs) than electronic bibliographic database (EBD) searches for systematic reviews of interventions, and to quantify the number of eligible ongoing trials. Study Design and Setting: We performed an evaluation study and based our search for RCTs on the eligibility criteria of a systematic review that focused on the underrepresentation of people with chronic kidney disease in cardiovascular RCTs. We conducted a combined search of and the WHO International Clinical Trials Registry Platform through the Cochrane Central Register of Controlled Trials to identify eligible RCTs registered up to June 1, 2023. We searched Cochrane Central Register of Controlled Trials, EMBASE, and MEDLINE for publications of eligible RCTs published up to June 5, 2023. Finally, we compared the search results to determine the extent to which the two sources identified the same RCTs. Results: We included 92 completed RCTs. Of these, 81 had results available. Sixty-six completed RCTs with available results were identified by both sources (81% agreement [95% CI: 71–88]). We identified seven completed RCTs with results exclusively by CTR search (9% [95% CI: 4–17]) and eight exclusively by EBD search (10% [95% CI: 5–18]). Eleven RCTs were completed but lacked results (four identified by both sources (36% [95% CI: 15–65]), one exclusively by EBD search (9% [95% CI: 1–38]), and six exclusively by CTR search (55% [95% CI: 28–79])). Also, we identified 42 eligible ongoing RCTs: 16 by both sources (38% [95% CI: 25–53]) and 26 exclusively by CTR search (62% [95% CI: 47–75]). Lastly, we identified four RCTs of unknown status by both sources. Conclusion: CTR searches identify a greater number of completed RCTs than EBD searches. Both searches missed some included RCTs. Based on our case study, researchers (eg, information specialists, systematic reviewers) aiming to identify all available RCTs should continue to search both sources. Once the barriers to performing CTR searches alone are targeted, CTR searches may be a suitable alternative.
Original languageEnglish
Article number111300
JournalJournal of Clinical Epidemiology
Publication statusPublished - 1 May 2024


  • Clinical trial register search
  • Clinical trial registry
  • Information retrieval
  • Randomized clinical trials
  • Randomized controlled trials
  • Systematic review

Cite this