Discriminative and Predictive Validity Assessment of the Quebec Task Force Classification

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Abstract
A prospective cohort study of workers with low back pain who had been absent from work for more than 4 weeks was conducted. To assess the discriminative and predictive validity of the Quebec Task Force Classification for workers during the subacute phase of disability from back pain. The Quebec Task Force Classification was designed for clinical decision making, prognosis establishment, quality of care evaluation, and scientific research in low back pain. For this study, 104 workers absent from work because of back pain were classified according to the first four categories of the Quebec Task Force Classification 4 weeks after their first day of work absence. They then were randomized into four treatment groups: standard care (control), clinical–rehabilitation intervention, occupational intervention, and the Sherbrooke model (a combination of the clinical–rehabilitation and occupational interventions). Functional status, pain level, and work status were assessed at baseline and after 1 year. Duration of full compensation and back-related costs were calculated over a mean follow-up period of 6.5 years. The discriminative validity of the Quebec Task Force Classification was evaluated using Kendall tau correlation coefficients. Predictive validity was evaluated using logistic regression analyses. Age, gender, comorbidities, body mass index, and treatment group were considered as potential confounders. Significant but low correlation coefficients were found between Quebec Task Force Classification categories and functional status scores at baseline. Subjects classified as having distal radiating pain (categories 3 and 4) at baseline were more likely to have a lower functional status, higher pain level, and no return to regular work at the 1-year follow-up evaluation. They also were more likely to accumulate more days of full compensation and to cost more after a mean follow-up period of 6.5 years. The Quebec Task Force Classification demonstrated good predictive ability by discriminating between subjects with and those without distal radiating pain.