Background: The Dermatology Life Quality Index (DLQI) is the most commonly used instrument for clinical evaluation of the impact on health-related quality of life (HRQOL) in dermatological research protocols. The DLQI's classical psychometric properties have been considered adequate in validation studies from several countries. However, the structure of the DLQI is a matter of discussion, especially concerning the dimensionality and informative properties of its questions according to the item response theory (IRT). Methods: Pooled data from studies in Brazil that utilized the DLQI to assess HRQOL in 14 dermatoses were reanalyzed. Classical psychometrical analysis, dimensionality assessment through parallel analysis and IRT (Samejima's ordinal model) analysis were performed. Results: The sample consisted of 1286 patients with a mean age of 47 years (SD = 16), and the proportion of women was 59% (765). The DLQI scores ranged from 0 to 29, with a median (p 25-p 75) of 5 (2-11). All items indicated significant correlations with the total DLQI score (rho > 0.54). The Cronbach's alpha result was 0.90 (CI 95% 0.89-0.91). Parallel analysis indicated a unidimensional factor structure. According to IRT analysis, items q6 (sports) and q7 (work/study) exhibited insufficient fit to the model (p < 0.01), while the items that indicated the best discrimination and information functions were q2 (embarrassment), q3 (shopping/gardening), q4 (clothing) and q5 (social/leisure). The ordination of the scores was confirmed for all items. Most items revealed non-uniform behavior according to sex, age and type of disease. Conclusions: The DLQI exhibits adequate psychometric reliability and a unidimensional structure for assessing HRQOL in Brazilian dermatological patients. The DLQI's performance varies in the assessment of HRQOL in heterogeneous samples.

Background Health-related quality of life assesses how diseases affect the daily life of people; there are several generic instruments for this assessment in dermatology. Skindex was created in 1996; it is a multidimensional instrument, aiming to encompass some psychological and social aspects not yet addressed by other questionnaires. Among its versions (Skindex-29, 16, and 17), Skindex-17 had not been validated in Brazil. Objectives To validate Skindex-17 for use in Brazilians with dermatological diseases. Methods This was a methodological, cross-sectional, and prospective study of 217 patients attended at the Dermatology Service Outpatient Clinic, Faculdade de Medicina de Botucatu - Universidade Estadual Paulista (Botucatu, SP, Brazil), from December 2017 to September 2019. The following were evaluated: content validity, filling time, internal consistency, dimensional structure, concurrent validity (DLQI), temporal stability, and responsiveness. Results The sample consisted of 71% women, mean age (SD) of 45 (16) years; phototypes II−IV accounted for 95% of the cases. Cronbach's alpha coefficients were 0.82 and 0.93 for the symptoms and psychosocial conditions, respectively. A high correlation was observed with the DLQI score: symptoms (rho = 0.69) and psychosocial conditions (rho = 0.75). The instrument's two-dimensional structure was confirmed through confirmatory factor analysis. Temporal stability (ICC > 0.9) and score responsiveness (p ≤ 0.02) were verified. The instrument was shown to be feasible in clinical practice due to the content validation performed by professionals and patients, as well as the low time spent completing it (< 5 min). Study limitations Single-center study, with patients exclusively from the public healthcare system. Conclusions Skindex-17 was shown to be a valid and consistent instrument for assessing quality of life among patients with dermatological diseases, in Brazil. Its two-dimensional structure was confirmed.

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