Study design: The Quebec Back Pain Disability Scale is a 20-item self-administered instrument designed to assess the level of functional disability in individuals with back pain. The scale was administered as part of a larger questionnaire to a group of 242 back pain patients. Follow-up data were obtained after several days and after 2 to 6 months.
Objectives: The goal of this study was to determine whether the Quebec scale is a reliable, valid, and responsive measure of disability in back pain, and to compare it with other disability scales.
Summary of background data: A number of functional disability scales for back pain are being used, but their conceptual validity is uncertain. Unlike most published instruments, the Quebec scale was constructed using a conceptual approach to disability assessment and empirical methods of item development, analysis, and selection.
Methods: The authors calculated test-retest and internal consistency coefficients, evaluated construct validity of the scale, and tested its responsiveness against a global index of change. Direct comparisons with the Roland, Oswestry, and SF-36 scales were carried out.
Results: Test-retest reliability was 0.92, and Cronbach's alpha coefficient was 0.96. The scale correlated as expected with other measures of disability, pain, medical history, and utilization variables, work-related variables, and socio-demographic characteristics. Significant changes in disability over time, and differences in change scores between patients that were expected to differ in the direction of change, were found.
Conclusions: The Quebec scale can be recommended as an outcome measure in clinical trials, and for monitoring the progress of individual patients participating in treatment or rehabilitation programs.