Minimal Important Difference (MID) of the Dermatology Life Quality Index (DLQI): Results from patients with chronic idiopathic urticaria

BACKGROUND The Dermatology Quality Life Index (DLQI) has seen widespread use as a health-related quality of life measure for a variety of dermatological diseases. The purpose of this study was to estimate the minimal important difference (MID) on the DLQI for patients with chronic idiopathic urticaria (CIU). METHODS Data from 2 Phase III clinical trials of patients (N = 476 for Study A; N = 468 for Study B) with CIU were analyzed separately to estimate the MID for the DLQI for these populations. Both distributional based and anchor based approaches were used for deriving estimates. The anchor based approach relied upon patient self assessments of pruritus severity; the distributional based approaches relied upon estimating the standard error of measurement, as well as one-half the standard deviation of the DLQI from each study. RESULTS The distributional approaches resulted in estimates of MID ranging from 2.24 to 3.10 for the two studies. The anchor based approach resulted in estimates of 3.21 and 2.97 for the two studies. CONCLUSION An MID for the DLQI in the range of 2.24 to 3.10 is recommended in interpreting results for patients with CIU.