 The study aimed to determine the optimal combination of databases needed for efficient searches in systematic reviews. The authors analyzed the actual retrieval from original searches for 58 published systematic reviews and found that the combination of Mbass, Medline, Web of Science Core Collection, and Google Scholar performed best, achieving an overall recall of 98.3 and 100% recall in 72% of systematic reviews. The study estimates that 60% of published systematic reviews do not retrieve 95% of all available relevant references as many fail to search important databases. Therefore, the authors recommend that optimal searches in systematic reviews should search at least in base, Medline, Web of Science, and Google Scholar as a minimum requirement to guarantee adequate and efficient coverage. This article was authored by Witcher M. Braemer, Melissa L. Reff Lefson, Joes Kleinan, and others.