title: Are English- and Chinese-language versions of the SF-6D equivalent? A comparison from a population-based study.
abstract: OBJECTIVE
  The goal of this study was to assess the equivalence of English- and Chinese-language versions of the SF-6D (a 6-dimensional health classification system based on the 36-Item Short Form Health Survey) using a model of equivalence proposed previously.
  
  
  METHODS
  We analyzed data from a previously published, cross-sectional, population-based survey of ethnic Chinese in Singapore, using linear regression models to adjust for the influence of potential confounding variables. Based on equivalence clinical trial methods, measurement (ie, scale) and item equivalence were assessed by comparing 90% CIs of differences in scores due to language with predefined equivalence margins, that corresponded to the minimum clinically important difference for SF-6D utility and item scores.
  
  
  RESULTS
  Data from 2,558 respondents (aged 21-65 years; 48.8% completed the English-language version) were analyzed. The utility scores of respondents using the English- or Chinese-language versions of the SF-6D had similar distribution patterns, with a mean (SD) utility score of 0.8 (0.12). Adjusted 90% CIs for differences in utility and item scores due to language fell within predefined equivalence margins, suggesting measurement and item level equivalence. The 90% CI for scale scores was -0.0089 to 0.0065 (range, 0.0154; equivalence margin, 0.033); the 90% CI for item scores varied from -0.0046 to -0.0020 (range, 0.0026; equivalence margin, 0.0036) for vitality to -0.0024 to 0.0037 (range, 0.0061; equivalence margin, 0.0088) for social functioning. Functional equivalence was suggested because the various aspects of equivalence proposed previously were demonstrated in this study.
  
  
  CONCLUSIONS
  English- and Chinese-language versions of the SF-6D demonstrated item, measurement, and functional equivalence in this population-based study comparing 2 widely used languages with very different linguistic structures. This suggests that English and Chinese SF-6D scores can be pooled, thus increasing the representativeness and power of studies using the SF-6D, and providing a basis for studies to value health by obtaining SF-6D utility scores in Asian populations.
authors.affiliation: Department of Pharmacy, National University of Singapore, Singapore.
authors.forename: Hwee-Lin
authors.initials: HL
authors.lastname: Wee
authors.forename: Yin-Bun
authors.initials: YB
authors.lastname: Cheung
authors.forename: Kok-Yong
authors.initials: KY
authors.lastname: Fong
authors.forename: Nan
authors.initials: N
authors.lastname: Luo
authors.forename: David
authors.initials: D
authors.lastname: Machin
authors.forename: Julian
authors.initials: J
authors.lastname: Thumboo
mesh_terms: D000328:Adult; D000368:Aged; D002681:China; D003431:Cross-Cultural Comparison; D005260:Female; D006304:Health Status; D006306:Health Surveys; D006801:Humans; D007802:Language; D008297:Male; D008875:Middle Aged; D011594:Psychometrics; D011788:Quality of Life; D012846:Singapore; D012923:Social Class