A comparative study on the measurement properties of Dermatology Life Quality Index (DLQI), DLQI‐Relevant and Skindex‐16*

Dermatology Life Quality Index (DLQI) and Skindex-16 are among the most commonly used dermatology-specific health-related quality-of-life (HRQoL) instruments. DLQI has two common scoring methods, the original and the DLQI-Relevant (DLQI-R) modification. Head-to-head comparisons of the measurement properties of the DLQI, DLQI-R and Skindex-16 are currently lacking.We aim to compare the measurement properties of the DLQI, DLQI-R and Skindex-16.We analysed data from 618 patients with self-reported physician-diagnosed dermatological conditions from a cross-sectional survey carried out in Hungary in early 2020. DLQI, DLQI-R and Skindex-16 were compared in terms of ceiling and floor effects, informativity, convergent validity and known-group validity.Mean DLQI, DLQI-R and Skindex-16 total scores were 3·76 ± 5·03, 4·11 ± 5·34 and 29·36 ± 26·62, respectively. Among patients with a DLQI/DLQI-R total score of zero, 64% reported problems on Skindex-16. Overall, 23-38% of patients with 'not relevant' responses on DLQI items 3 (shopping/home/gardening), 7 (working/studying), 8 (interpersonal problems) and 9 (sexual difficulties) reported problems on their corresponding Skindex-16 items. Average relative informativity (Shannon's evenness index) was the highest for Skindex-16 (0·85), followed by DLQI-R (0·66) and DLQI (0·54). DLQI, DLQI-R and Skindex-16 demonstrated similar convergent validity. DLQI was able to better discriminate between known groups of patients based on overall skin-related HRQoL impairment, whereas DLQI-R and Skindex-16 performed better with respect to self-perceived health status.Skindex-16 seems to be more sensitive than DLQI/DLQI-R in capturing mild impairment in HRQoL. Our findings help to provide a fuller understanding of the difference between DLQI, DLQI-R and Skindex-16 and support the informed choice of instrument for clinical and research purposes.