Responsiveness and sensitivity to change of SLE disease activity measures

The ability of outcome measures to detect change over time is critical fbr their usefulness in clinical trials. Two concepts are applied in the assess ment of evaluative instruments: We endorse the recommendation that a distin ction be made between sensitivity and responsiveness. Sensitivity to change refers to the capacity of instruments to measure change statistically. Sen sitivity statistics relate the magnitude of observed change to some measure of variablity and are essentially signal-to-noise ratios. Responsiveness a ddresses the detection of clinically relevant change. The methodology is st ill evolving but a common approach has been to correlate the observed chang e 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 av ailable evidence does not allow preference for one instrument over the othe rs. Little research has been done on the responsiveness of these measures. This article reviews the methodological concepts in measuring clinical chan ge and summarizes reports on sensitivity and responsiveness of lupus activi ty scores.