Mapping DLQI on EQ-5D in psoriasis: transformation of skin-specific health-related quality of life into utilities

In many countries, utility measures are required for allocation decisions. Unlike the EuroQoL-5D (EQ-5D), the dermatology life quality index (DLQI) has not been developed for the derivation of utilities. Purpose of this study was to develop and test an algorithm for the transformation of DLQI scores into utilities. Pre-existing data of two cross-sectional studies (for development, n = 1,511; for cross-validation n = 2,009) of German psoriasis patients were reanalyzed. Both EQ-5D global score and EQ-5D visual analogue scale (VAS) were used as utility measures. Correlations were computed to identify predictors of EQ-5D utilities. Linear stepwise regressions were conducted using DLQI and further possible predictors to find the optimal mapping algorithm. Using only DLQI as predictor resulted in coefficients of determination of r2 = 0.235 (EQ-5D global score) and r2 = 0.242 (EQ-5D VAS). In the final algorithm, seven predictors were included which correctly predicted EQ-5D VAS for 60.4 % (development database) and 60.8 % of all patients (cross-validation database) within a range of ±15 units. The algorithm explained 31.3 % of the EQ-5D variance in the development database and 26.8 % in the cross-validation database. In conclusion, mapping of DLQI on EQ-5D in psoriasis patients has severe limitations in validity and clinical relevance.