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Electronic letters published:
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Making Difficult Choices
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Susan Galandiuk, MD Price Institute of Surgical Research, University of Louisville, ,KY 40202, Suhal S. Mahid, Kyle S. Minor, Susan Galandiuk
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s0gala01{at}gwise.louisville.edu Susan Galandiuk, et al.
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TO THE EDITOR: Del Brutto and colleagues (1) provide a well thought out meta-analysis, in which they state clear inclusion criteria and three authors independently reviewed articles. Over the past decade, meta- analyses have been increasingly used in medicine. In addition to providing a more precise estimate of the effect of a treatment or exposure, properly conducted meta-analyses combine studies to show a less biased estimate than traditional reviews (2). One way of achieving this less biased estimate is by utilizing multiple databases when searching for studies that meet meta-analysis inclusion criteria (3). Failure to search multiple health databases can result in missing up to half of the relevant literature (4). Embase and Medline are the two most comprehensive databases used in meta-analyses. Embase contains over 18 million records, including an index of over 7,000 journals from 70 countries. It is recognized as an important source of pharmacological and biomedical literature. It is also a relevant source of negative studies, since European and non-English journals are said to be more likely to publish negative findings. Despite the recognized importance of searching Embase, many meta-analysts [including Del Brutto et al. (1)] neglect it in their search for relevant articles. We believe that cost is an important reason for this lack of use. While Medline is free of charge and available to anyone by internet, Embase is more difficult to access and considerably more expensive. Meta- analysts have to make the difficult choice of whether they should use funding to access Embase. For researchers without the necessary funding to access pay-for-view databases, several options remain. An important source for obtaining negative studies is by hand searching gray literature (defined as abstracts in major meetings and symposiums, newsletters, theses, etc.). It has been estimated that omitting gray literature from meta-analyses can affect analysis outcome by as much as 15% (5). Searching multiple databases is an important step in retrieving relevant articles for meta-analyses. Utilizing as many sources of information as possible reduces bias. Pay-for-view databases make it more difficult for researchers to acquire relevant information and, in turn, may compromise meta-analyses. Suhal S. Mahid, MRCS Kyle S. Minor, BA Susan Galandiuk, MD Price Institute of Surgical Research, University of Louisville, Louisville, KY 40202 References 1. Del Brutto OH, Roos KL, Coffey CS, Garcia HH. Meta-analysis: Cysticidal drugs for Neurocysticercosis: Albendazole and Praziquantel. Ann Intern Med. 2006;145:43-51. [PMID: 16818928] 2. Mahid SS, Hornung CA, Minor KS, Turina M, Galandiuk S. Quality assessment of systematic reviews and meta-analysis for the surgeon scientist. Br J Surg. 2006 (in press). 3. Sampson M, Barrowman NJ, Moher D, Klassen TP, Pham B, Platt R, et al. Should meta-analysts search Embase in addition to Medline? J Clin Epidemiol. 2003;56:943-55. [PMID: 14568625] 4. Dickersin K, Scherer R, Lefebvre C. Identifying relevant studies for systematic reviews. BMJ. 1994;309:1286-91. [PMID: 7718048] 5. McAuley L, Pham B, Tugwell P, Moher D. Does the inclusion of grey literature infleunce estimates of intervention effectiveness reported in meta-analyses? Lancet. 2000;356:1228-31. [PMID: 11072941] Conflict of Interest:None declared |
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