Cross-cultural validation and analysis of responsiveness of the QUALIOST^®: QUAlity of Life questionnaire In OSTeoporosis

Abstract

Abstract Background The QUALIOST® was designed for use with the SF-36 to measure established osteoporosis-specific quality of life (QoL). The reliability (internal consistency and test-retest) and validity of the questionnaire were established in a stand-alone psychometric validation study. The objective of this paper is to provide additional information on the instrument's responsiveness using clinical trial data, along with the reliability and validity of translated versions. Methods The Spinal Osteoporosis Therapeutic Intervention (SOTI) was an international clinical trial comparing strontium ranelate to placebo on the occurrence of new vertebral fracture in patients with postmenopausal osteoporosis. QoL was a secondary endpoint, assessed using the SF-36 and QUALIOST® at baseline and every six months, with the main analysis at 3-year follow-up. Questionnaire acceptability, analysis of the hypothesised structure, internal consistency reliability and responsiveness to clinical change over time were assessed at the 3-year follow up. Results 1592 patients from 11 countries completed at least one QoL questionnaire. The psychometric properties of the questionnaires were assessed on cross-sectional (N = 1486) and longitudinal (N = 1288) data. Item discriminant validity of the QUALIOST® was excellent, as was item convergent validity, with 100% of item-scale correlations being above the 0.40 level. Internal consistency reliability was also extremely good, with high Cronbach's alpha scores above the 0.70 benchmark. Responsiveness results were consistent for all QUALIOST® scores, indicating that greater decreases in QoL corresponded to greater numbers of fractures experienced. QUALIOST® scores also differed according to the type of fracture suffered. This was demonstrated by increased effect sizes for more severe vertebral fractures (clinical vertebral and painful vertebral). In comparing responsiveness, the QUALIOST® scores were generally more consistent than those of the SF-36. Most notably, the QUALIOST® was more responsive with regard to painful vertebral fractures than the SF-36. Conclusion The QUALIOST® is a reliable and valid tool for measuring QoL in postmenopausal osteoporotic women. Being available in several validated language versions, it is ready to be used in a variety of settings, including international clinical trials.