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To the Editor: In their meta-analysis of randomized controlled trials of folic acid supplementation and risk of cardiovascular disease, Dr Bazzano and colleagues¹ provided a clear description of their inclusion criteria and study selection process. Using multiple databases when searching for studies that meet meta-analysis inclusion criteria may help avoid selection bias.² Failure to search multiple health databases can result in missing up to half of the relevant literature.³

EMBASE and MEDLINE are the 2 most comprehensive databases used in meta-analyses. EMBASE focuses on drugs and pharmacology and contains more than 18 million records, including an index of more than 7000 journals from 70 countries. It may be a relevant source of negative studies, because European and non–English-language journals may be more likely to publish negative findings. However, Bazzano et al limited their literature search to MEDLINE. In addition, an important source for obtaining negative studies is hand searching of . . . [Full Text of this Article]

Suhal S. Mahid, MRCS, PhD
ssmahi01@louisville.edu

Kyle S. Minor, BA; Susan Galandiuk, MD
Price Institute of Surgical Research
University of Louisville
Louisville, Ky

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