Responsiveness and sensitivity to change of SLE disease activity measures.

The ability of outcome measures to detect change over time is critical for their usefulness in clinical trials. Two concepts are applied in the assessment of evaluative instruments: We endorse the recommendation that a distinction be made between sensitivity and responsiveness. Sensitivity to change refers to the capacity of instruments to measure change statistically. Sensitivity statistics relate the magnitude of observed change to some measure of variablity and are essentially signal-to-noise ratios. Responsiveness addresses the detection of clinically relevant change. The methodology is still evolving but a common approach has been to correlate the observed change in scores with external standards that are believed to indicate clinical relevance (e.g., physician- or patient-based transition scales). Sensitivity to change and responsiveness of SLE activity indices have been addressed in a small number of studies. These indicate that the most widely used systems (SLEDAI. SLAM, BILAG) are sensitive to change although the available evidence does not allow preference for one instrument over the others. Little research has been done on the responsiveness of these measures. This article reviews the methodological concepts in measuring clinical change and summarizes reports on sensitivity and responsiveness of lupus activity scores.