OBJECTIVES: Embase, PubMed, and Cochrane Library are the key sources for evidence-based healthcare researchers for literature searches. There is a certain degree of reference overlap between these databases; however, no explicit details on overlap are available. Therefore, we analyzed the level of overlap and associated risk of missing studies.

METHODS: We conducted two searches on mesothelioma and lymphoma as case examples and followed a step-by-step approach to verify citations manually across databases. We developed a search strategy for the Embase.com interface using industry-standard search filters and translated it for use in PubMed and Cochrane.

RESULTS: Embase and PubMed identified 861 and 179 citations, respectively, for mesothelioma. We observed some critical variations. Of the 179 PubMed citations, 4 were missing in Embase (both in search output and content archive), which refutes the post-2010 theoretical consensus that all MEDLINE citations reside in Embase. Similarly, among the 515 and 250 citations retrieved from Embase and PubMed for lymphoma, 12 MEDLINE citations were missing in Embase. We further noticed that all citations missing in Embase were published in the last 1-3 years, so potentially not missed due to time-lag but due to coverage of different journals. This highlights the necessity to search PubMed separately for its overall content rather than considering Embase as a one-stop shop. The Cochrane search identified 139 and 101 citations for mesothelioma and lymphoma, respectively. As Cochrane includes publications related to trials from Embase and PubMed (either through autofeed or crowdsourcing), 100% of the Cochrane records were duplicates with Embase and Medline search output. This questions the relevance of conducting independent searches on Cochrane.

CONCLUSIONS: The results suggest that researchers should view Embase and PubMed as independent sources to be searched without dependence on cross-database coverages. The relevance of Cochrane to cover scientific evidence beyond trials needs further testing.