Does being bilingual in English and Chinese influence responses to Quality-of-Life scales?

BACKGROUND. It is not known if the inclusion of bilinguals affects the results of research using Quality-of-Life (QoL) scales. OBJECTIVE. To determine the influence of bilingualism on responses to a QoL scale. RESEARCH DESIGN. In this cross sectional study, a population-based, disproportionately stratified random sample of monolingual and bilingual ethnic Chinese completed the Short-Form 36 Health Survey (SF-36) in English or Chinese (representing an alphabet and pictogram based language respectively). Cumulative logit regression models were used to assess the influence of bilingualism on SF-36 scores, while adjusting for the influence of questionnaire language and known determinants of QoL. RESULTS. English or Chinese SF-36 versions were completed by 1331 and 1380 subjects respectively (49% female, aged 21-65 years, 1366 bilingual, 501 English monolingual, 844 Chinese monolingual), with response rates exceeding 85%. Fifty percent of subjects were bilingual. Bilinguals differed from monolin-guals in known determinants of QoL, being younger, better educated, and having fewer chronic medical conditions, and had SF-36 scores up to 8 points higher than monolin-guals. After adjusting for these differences, bilingualism did not influence scores for any of eight SF-36 scales, whereas questionnaire language influenced scores for four scales. Use of the English SF-36 was associated with higher scores for General Health, Vitality, Role Emotional and Mental Health Scales (odds ratios 1.35-1.41), though the magnitude of these odds ratios suggests this association may not be clinically important. CONCLUSION. Bilingualism did not influence responses to a QoL scale in this large, population-based study of subjects fluent in an alphabet and/or pictogram based language.