English translation and validation of the SarQoL®, a quality of life questionnaire specific for sarcopenia

Background: the first quality of life questionnaire specific to sarcopenia, the SarQoL (R), has recently been developed and validated in French. To extend the availability and utilisation of this questionnaire, its translation and validation in other languages is necessary. Objective: the purpose of this study was therefore to translate the SarQoL (R) into English and validate the psychometric properties of this new version. Design: cross-sectional. Setting: Hertfordshire, UK. Subjects: in total, 404 participants of the Hertfordshire Cohort Study, UK. Methods: the translation part was articulated in five stages: (i) two initial translations from French to English; (ii) synthesis of the two translations; (iii) backward translations; (iv) expert committee to compare the backward translations with the original questionnaire and (v) pre-test. To validate the English SarQoL (R), we assessed its validity (discriminative power, construct validity), reliability (internal consistency, test-retest reliability) and floor/ceiling effects. Results: the SarQoL (R) questionnaire was translated without any major difficulties. Results indicated a good discriminative power (lower score of quality of life for sarcopenic subjects, P = 0.01), high internal consistency (Cronbach's alpha of 0.88), consistent construct validity (high correlations found with domains related to mobility, usual activities, vitality, physical function and low correlations with domains related to anxiety, self-care, mental health and social problems) and excellent test-retest reliability (intraclass coefficient correlation of 0.95, 95% CI 0.92-0.97). Moreover, no floor/ceiling has been found. Conclusions: a valid SarQoL (R) English questionnaire is now available and can be used with confidence to better assess the disease burden associated with sarcopenia. It could also be used as a treatment outcome indicator in research.