Cross-cultural Adaptation and Validation of the Quebec Back Pain Disability Scale to European Portuguese Language

Abstract

Cross-cultural adaptation and psychometric testing. To conduct the cross-cultural adaptation of the Quebec Back Pain Disability Scale (QBPDS) and investigate its reliability and validity in patients with chronic low back pain (CLBP). The QBPDS is one of the most commonly used scales to evaluate functional incapacity resulting from low back pain. Although measuring disability is an important outcome in physiotherapy care, there is no previous research relating to the cultural adaptation and psychometric testing of the QBPDS in the Portuguese-speaking population. The questionnaire was first translated and back-translated in accordance with the published guidelines. The Portuguese version of the QBPDS was then pilot tested in a Portuguese sample of 40 patients with CLBP. Psychometric properties were evaluated in a new sample of 132 patients with CLBP. Exploratory factor analysis was performed to confirm its unidimensionality. Reliability was evaluated through internal consistency and reproducibility, using the Cronbach α and intraclass correlation coefficient, respectively. Construct validity was assessed with correlations between the QBPDS and the Roland-Morris Disability Questionnaire and between the QBPDS and the visual analogue pain scale for convergent validity and pain localization for discriminative validity, using the Spearman correlation analysis and the Mann-Whitney test. Exploratory factor analysis revealed the existence of one major factor that explains 52.1% of the variance. One-week test-retest reliability was 0.7, and internal consistency was 0.95. The QBPDS correlated strongly with the Roland-Morris Disability Questionnaire (0.62; P < 0.001), moderately with pain (0.38; P < 0.001), and shows capability to discriminate between patients with localized and referred pain (U = 1218; P < 0.0005). The reliability and construct validity of the Portuguese version of the QBPDS are acceptable to assess functional status of Portuguese-speaking patients with CLBP. .