RESPONSIVENESS OF FUNCTIONAL STATUS IN LOW-BACK-PAIN - A COMPARISON OF DIFFERENT INSTRUMENTS

This study compares the responsiveness of three instruments of functio nal status: two disease-specific questionnaires (Oswestry and Roland D isability Questionnaires), and a patient-specific method (severity of the main complaint). We compared changes over time of functional statu s instruments with pain rated on a visual analog scale. Two strategies for evaluating the responsiveness in terms of sensitivity to change a nd specificity to change were used: effect size statistics and receive r-operating characteristic method. We chose global perceived effect as external criterion. A cohort of 81 patients with non-specific low bac k pain for at least 6 weeks assessed these measures before and after 5 weeks of treatment. According to the external criterion 38 patients i mproved. The results of both strategies were the same. All instruments were able to discriminate between improvement and non-improvement. Th e effect size statistics of the instruments were higher in the improve d group than in the non-improved group. For each instrument the receiv er-operating characteristic curves showed some discriminative ability. The curves for the Roland Questionnaire and pain were closer to the u pper left than the curves for the other instruments. The sensitivity t o change of the rating of Oswestry Questionnaire was lower than that o f the other instruments. The main complaint was not very specific to c hange. The two strategies for evaluating the responsiveness were very useful and appeared to complement each other.