a1 Canadian Agency for Drugs and Technologies in Health
a2 Canadian Agency for Drugs and Technologies in Health email: Juliep@cadth.ca
a3 Private Universität für Gesundheitswissenschaften, Medizinische Informatik und Technik GmbH University of Ottawa
a4 Canadian Agency for Drugs and Technologies in Health
a5 Cochrane Effective Practice and Organization of Care (EPOC) Group
a6 Canadian Agency for Drugs and Technologies in Health
a7 Canadian Agency for Drugs and Technologies in Health and University of Ottawa
a8 Ottawa Hospital Research Institute
a9 Canadian Agency for Drugs and Technologies in Health
Objectives: The English language is generally perceived to be the universal language of science. However, the exclusive reliance on English-language studies may not represent all of the evidence. Excluding languages other than English (LOE) may introduce a language bias and lead to erroneous conclusions.
Study Design and Setting: We conducted a comprehensive literature search using bibliographic databases and grey literature sources. Studies were eligible for inclusion if they measured the effect of excluding randomized controlled trials (RCTs) reported in LOE from systematic review-based meta-analyses (SR/MA) for one or more outcomes.
Results: None of the included studies found major differences between summary treatment effects in English-language restricted meta-analyses and LOE-inclusive meta-analyses. Findings differed about the methodological and reporting quality of trials reported in LOE. The precision of pooled estimates improved with the inclusion of LOE trials.
Conclusions: Overall, we found no evidence of a systematic bias from the use of language restrictions in systematic review-based meta-analyses in conventional medicine. Further research is needed to determine the impact of language restriction on systematic reviews in particular fields of medicine.
This review was led by the Canadian Agency for Drugs and Technologies in Health (CADTH). CADTH is an independent, not-for-profit agency funded by Canadian federal, provincial and territorial governments to provide credible, impartial advice and evidence-based information about the effectiveness of drugs and other health technologies to Canadian healthcare decision makers. For more information, visit www.cadth.ca.