title: What contributions do languages other than English make on the results of meta-analyses?
abstract: Including only a portion of all available evidence may introduce systematic errors into the meta-analytic process and threaten its validity. We set out to examine whether language restricted meta-analyses, compared to language inclusive meta-analyses, provide different estimates of the effectiveness of interventions evaluated in randomized trials. We identified and retrieved all 79 meta-analyses from several disease areas in which explicit eligibility criteria regarding trial selection were reported. General characteristics and quality of reporting of the meta-analyses were assessed using a validated instrument. We explored the effects of language of publication of the randomized trials on the quantitative results using logistic regression analyses. Language restricted meta-analyses, compared to language inclusive meta-analyses, did not differ with respect to the estimate of benefit of the effectiveness of an intervention (ROR = 0.98; 95% CI: 0.81-1.17). These results were also robust after a series of sensitivity analyses. This study provides no evidence that language restricted meta-analyses lead to biased estimates of intervention effectiveness. We encourage others to replicate this study using different sampling frames, clinical topics and interventions.
authors.affiliation: Thomas C. Chalmers Center for Systematic Reviews, Children's Hospital of Eastern Ontario Research Institute, Ontario, Ottawa, Canada. dmoher@uottawa.ca
authors.forename: D
authors.initials: D
authors.lastname: Moher
authors.forename: B
authors.initials: B
authors.lastname: Pham
authors.forename: T P
authors.initials: TP
authors.lastname: Klassen
authors.forename: K F
authors.initials: KF
authors.lastname: Schulz
authors.forename: J A
authors.initials: JA
authors.lastname: Berlin
authors.forename: A R
authors.initials: AR
authors.lastname: Jadad
authors.forename: A
authors.initials: A
authors.lastname: Liberati
mesh_terms: D006801:Humans; D007802:Language; D016015:Logistic Models; D015201:Meta-Analysis as Topic; D017063:Outcome Assessment, Health Care; D016032:Randomized Controlled Trials as Topic; D015983:Selection Bias