Searching two or more databases decreased the risk of missing relevant studies: a metaresearch study

Background and Objectives: Assessing changes in coverage, recall, review, conclusions and references not found when searching fewer databases. Methods: In randomly selected 60 Cochrane reviews, we checked included study publications' coverage (indexation) and recall (find -ability) using different search approaches with MEDLINE, Embase, and CENTRAL and related them to authors' conclusions and certainty. We assessed characteristics of unfound references. Results: Overall 1989/2080 included references, were indexed in > 1 database (coverage = 96%). In reviews where using one of our search approaches would not change conclusions and certainty (n = 44-54), median coverage and recall were highest (range 87.9%-100.0% and 78.2%-93.3%, respectively). Here, searching > 2 databases reached O95% coverage and > 87.9% recall. In reviews with unchanged conclusions but less certainty (n = 2-8): 63.3%-79.3% coverage and 45.0%-75.0% recall. In reviews with opposite conclusions (n = 1-3): 63.3%-96.6% and 52.1%-78.7%. In reviews where a conclusion was no longer possible (n = 3-7): 60.6%-86.0% and 20.0%-53.8%. The 265 references that were indexed but unfound were more often abstract less (30% vs. 11%) and older (28% vs. 17% published before 1991) than found references. Conclusion: Searching >= 2 databases improves coverage and recall and decreases the risk of missing eligible studies. If researchers suspect that relevant articles are difficult to find, supplementary search methods should be used. (C) 2022 The Author(s). Published by Elsevier Inc.

Automated summary

This study assesses the impact of different database search methods on research outcomes. The results indicate that searching more than two databases improves coverage and recall and reduces the risk of missing eligible studies.