Assessment of the Dermatology Life Quality Index (DLQI) in a homogeneous population under lifetime arsenic exposure.

PURPOSE: The psychometric property of the Dermatology Life Quality Index (DLQI) is underappreciated in public health settings. Our study aimed to assess the reliability, validity, and measurement invariance of DLQI in a homogeneous population with arsenic-related skin lesions and symptoms. METHODS: A cross-sectional study was conducted in communities under lifetime arsenic exposure. The DLQI was measured through a face-to-face interview. Skin examinations were performed by certificated dermatologists. The intensity of itching was measured by a numerical rating scale. Reliability, structural validity, and measurement invariance were determined using classical and modern test theories, including confirmatory factor analysis and item response models. RESULTS: 465 participants with arsenic-related skin lesions and symptoms completed the DLQI assessment. The Cronbach's alpha was 0.79, and the split-half reliability was 0.77. A two-factor model exhibited the best model fit among models evaluated, but local dependencies among items were identified. The model showed good root mean square error of approximation (0.031) and acceptable Tucker-Lewis index (0.92). Multi-group confirmatory factor analysis showed no measurement invariance across subgroups of age, gender, ethnicity, and intensity of itching. CONCLUSIONS: The DLQI had acceptable psychometric properties, but measurement invariance was not observed across different groups of participants.