The rating scale preference measure as an evaluative measure in systemic lupus erythematosus

Preference measures may be useful tools to assess patients' overall health-related quality of life. We studied the validity and sensitivity to change of the rating scale preference measure in patients with systemic lupus erythematosus (SLE), and compared its properties with those of the patient global assessment of SLE activity, in a prospective longitudinal observational study of changes in the symptoms and clinical disease activity of 23 patients. Patients were assessed every two weeks for up to 40 weeks. Construct validity was assessed by the strength of correlations between changes over time in the rating scale preference measure and patient global assessment and changes in the physician global assessment, Systemic Lupus Activity Measure (SLAM), European Consensus Lupus Activity Measure (ECLAM), the British Isles Lupus Assessment Group index (BILAG), and Systemic Lupus Erythematosus Disease Activity Index (SLEDAI). Changes in the rating scale were more highly correlated with changes in each of these standards than were changes in the patient global assessment, demonstrating the construct validity of this measure. Sensitivity to change was measured using the two-week interval of greatest change in either the physician global assessment or the SLE activity measures as standards. The rating scale preference measure was less sensitive to change than the patient global assessment when tested against four different standards. The sensitivity to change of the rating scale was less than one-half that of the patient global assessment when either the SLAM or ECLAM was used as the standard. Although these results support the validity of the rating scale as a measure of health-related quality of life in patients with SLE, its limited sensitivity to change may make it less attractive as an endpoint measure in clinical trials.