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10.09.2018 | Ausgabe 12/2018

Quality of Life Research 12/2018

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

Quality of Life Research > Ausgabe 12/2018
Yi Xiao, Xiaoyan Huang, Danrong Jing, Yuzhou Huang, Xingyu Zhang, Zhihao Shu, Zhijun Huang, Juan Su, Jie Li, Jianglin Zhang, Mingliang Chen, Xiang Chen, Minxue Shen
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Electronic supplementary material

The online version of this article (https://​doi.​org/​10.​1007/​s11136-018-1969-2) contains supplementary material, which is available to authorized users.



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.


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.


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.


The DLQI had acceptable psychometric properties, but measurement invariance was not observed across different groups of participants.

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Scree plot of the exploratory factor analysis. Two common factors with eigenvalue>1.0 were identified. The third common factor had marginally significant eigenvalue of 0.99 (TIF 106 KB)
Item characteristic curve and item information function of the unidimensional item response model. The IRT was established for a unidimensional model. Each Item characteristic curve describes the item-specific relationship between the ability level (X-axis) and probability of endorsing a certain response (Y-axis). Black, blue, green, and magenta lines signify 0, 1, 2, and 3, respectively. Ability in the item response theory model practically (though not exclusively) ranged from −3 to +3. The dash lines signify item information functions, which indicate the precision of the items (TIF 253 KB)
Item characteristic curve and item information function of the bi-dimensional item response model. The IRT was established for a bi-dimensional model. Symbols are identical to Figure S2 (TIF 87 KB)
Supplementary material 4 (DOCX 18 KB)
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