International Journal of Technology Assessment in Health Care

METHODS

THE EFFECT OF ENGLISH-LANGUAGE RESTRICTION ON SYSTEMATIC REVIEW-BASED META-ANALYSES: A SYSTEMATIC REVIEW OF EMPIRICAL STUDIES

Andra Morrisona1, Julie Polisenaa2, Don Husereaua3, Kristen Moultona4, Michelle Clarka4, Michelle Fiandera5, Monika Mierzwinski-Urbana6, Tammy Clifforda7, Brian Huttona8 and Danielle Rabba9

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

Abstract

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.

Footnotes

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.