Responsiveness of generic and specific measures of health outcome in low back pain

Study Design. A longitudinal study using patient questionnaires was perform ed. Objective. To compare the discriminatory power and responsiveness of the Ab erdeen Back Pain Scale (ABPS), the Poland Disability Questionnaire (RDQ), a nd the EuroQol in patients with low back pain. Summary of Background Data. A number instruments specific to low back pain have not been compared for measurement properties. The EuroOol is a widely used generic instrument that has not been compared with specific instrument s in patients with back pain. Methods. A questionnaire incorporating the Aberdeen Back Pain Scale, the Po land Disability Questionnaire, and the EuroOol was completed by patients ta king part in a clinical trial of exercise treatments for back pain. Patient s completed follow-up questionnaires at 6 weeks, 6 months, and 1 year. The discriminatory power of these instruments was assessed against variables re lating to activity limitations, medication, and comorbidity. Responsiveness was assessed using standardized response means. Results. The questionnaire was completed by 187 patients taking part in the clinical trial. The Aberdeen instrument was found to be the most powerful at discriminating between different groups of patients on variables relatin g to activity limitations, medication, and comorbidity. The specific instru ments demonstrated good levels of responsiveness, with the Aberdeen instrum ent producing the largest standardized response means. The Aberdeen instrum ent was more responsive to the smaller changes experienced by the control g roup, but was less powerful than the Roland at measuring differences in the levels of change between the two groups of patients at two of the three fo llow-up assessments in the trial. The EuroOol demonstrated a moderate level of responsiveness. Conclusions. The two specific instruments are capable of greater levels of discrimination between groups of patients, and are more responsive over tim e than the generic EuroOol. The Aberdeen instrument performed most satisfac torily in relation to these criteria, but the Roland instrument was more se nsitive to differences between the two groups in the clinical trial. The me asurement properties of these two instruments reflect their origin: The Abe rdeen instrument is based on clinical questions, whereas the Poland instrum ent is based on the generic Sickness Impact Profile. Instrument content sho uld be carefully considered when selecting instruments for applications, in cluding clinical trials.