Table 1 shows the number and frequency of publications in other languages with more than 0.5 percent penetration. Using a literature search module for randomized controlled trials, 11 a search in Medline from 1996 to May 25, 2012, found that of 2,982,047 citations, 92 percent were published in English. 4 - 10 Nevertheless, excluding studies solely based on language runs counter to the concept of systematic review, of including all known evidence, particularly as investigators are being encouraged to include non-peer-reviewed and other studies in the grey literature. 1, 3 However, numerous other studies have found that excluding non-English publications may not result in substantial bias (changes in estimates of treatment effects). Thus, in most instances, EPC reports may be at risk of selection bias based on language (if there is reason to suspect differential publication of studies in English language and non-English journals) 1 and may not be following Standard 3.2.6 from the recent Institute of Medicine's (IOM) “Finding What Works in Health Care: Standards for Systematic Reviews,” 2 “Search for studies reported in languages other than English if appropriate.” The IOM report notes that there is some known evidence of language bias (e.g., investigators in Germany may be more likely to publish their negative results in German language publications and their positive results in English language publications). One included German- and French-language studies for nonoperative interventions (which were sparse), but only English-language publications for operative treatments “due to lack of translation resources.” Three of the CERs wrote that the language restriction was due to lack of resources or prohibitive translation costs, despite the recognition in one CER “that requiring studies to be published in English could lead to bias.” One placed no language restriction on comparative studies but included only English-language cohort studies. Two did not report language restriction in their methods chapter and included one study each in Dutch and German. Four explicitly did not impose any language restriction. Among 28 other recent Comparative Effectiveness Reviews (CERs) with final or draft documents downloadable from the AHRQ Web site, 20 were restricted to English-language publications. One report included studies in languages for which the EPC had “available fluency” and only one reported not restricting by language.
In a sample of 10 recent Evidence Reports (numbers 189-198), 8 were restricted to English-language publications. Systematic reviews conducted by the Agency for Healthcare Research and Quality (AHRQ) Evidence-based Practice Centers (EPCs) most commonly restrict literature searches to English language publications.
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