Equivalence of Measurement Properties of the Dermatology Life Quality Index (DLQI) Across 13 European Countries
Author(s)
Sam Salek, RPh, PhD1, Jeffrey R. Johns2, Faraz Mahmood Ali, MBBCh PhD MRCP(Derm)3, Florence Dalgard, MD, PhD4, Jörg Kupfer, PhD Dr. Dipl-Psych5, Andrew Y Finlay, MD3.
1School of Life and Medical Sciences, University of Hertfordshire, Hatfield, United Kingdom, 2Cardiff, United Kingdom, 3Division of Infection and Immunity, Cardiff University, Cardiff, United Kingdom, 4National Center for Dual Diagnosis, Innlandet Hospital Trust, Brumundal, Brumundal, Norway, 5Institute of Medical Psychology, Justus Liebig University, Giessen, Giessen, Germany.
1School of Life and Medical Sciences, University of Hertfordshire, Hatfield, United Kingdom, 2Cardiff, United Kingdom, 3Division of Infection and Immunity, Cardiff University, Cardiff, United Kingdom, 4National Center for Dual Diagnosis, Innlandet Hospital Trust, Brumundal, Brumundal, Norway, 5Institute of Medical Psychology, Justus Liebig University, Giessen, Giessen, Germany.
OBJECTIVES: The Dermatology Life Quality Index (DLQI) is the most widely used tool to measure burden of skin diseases and assess intervention effectiveness. It is embedded in national guidelines and disease registries in >45 countries and available in >138 translations. The study objective was to examine the psychometric properties of the DLQI across 13 European languages.
METHODS: Data were analysed from a cross-sectional study conducted in 13 European languages where up to 250 consecutive adult out-patients were recruited from 15 dermatology clinics. Parallel analysis, confirmatory factor analysis (CFA), Very Simple Structure (VSS) and Velicer's MAP-criterion were performed across datasets of each country and multigroup CFA (MGCFA) across all countries. Known-group analysis was performed of DLQI sum-score against physician assessed severity, and EQ-5D-VAS score quartiles by country using the Jonckheere-Terpstra test.
RESULTS: From 3,635 patients, 3,408 patients completed the DLQI questionnaire with no missing data. The commonest conditions reported were psoriasis (17.4%), non-melanoma skin cancer (10.8%), infection of the skin (6.7%), hand eczema (6.2%), acne (6.2%), nevi (5.0%), atopic dermatitis (4.5%), benign skin tumors (4.2%), and eczema (contact dermatitis) (4.1%). All countries’ DLQI data showed unidimensionality from parallel analysis, VSS and MAP, and very good fits to the 1-factor CFA model with CFI, TLI values all >0.97 (COSMIN criteria). MGCFA indicated different country translations of the DLQI conceptualize the same construct, are all unidimensional with equality of factor loadings. Known-group analysis of DLQI versus disease severity and versus EQ-5D VAS quartiles were significant for every country (all p<0.025).
CONCLUSIONS: Excellent psychometric properties were present across all 13 languages examined. Unidimensionality of the DLQI construct was confirmed and the DLQI is able to differentiate between levels of disease severity and EQ-5D levels across all these languages. This adds further confidence in the appropriateness of using the DLQI across this range of languages.
METHODS: Data were analysed from a cross-sectional study conducted in 13 European languages where up to 250 consecutive adult out-patients were recruited from 15 dermatology clinics. Parallel analysis, confirmatory factor analysis (CFA), Very Simple Structure (VSS) and Velicer's MAP-criterion were performed across datasets of each country and multigroup CFA (MGCFA) across all countries. Known-group analysis was performed of DLQI sum-score against physician assessed severity, and EQ-5D-VAS score quartiles by country using the Jonckheere-Terpstra test.
RESULTS: From 3,635 patients, 3,408 patients completed the DLQI questionnaire with no missing data. The commonest conditions reported were psoriasis (17.4%), non-melanoma skin cancer (10.8%), infection of the skin (6.7%), hand eczema (6.2%), acne (6.2%), nevi (5.0%), atopic dermatitis (4.5%), benign skin tumors (4.2%), and eczema (contact dermatitis) (4.1%). All countries’ DLQI data showed unidimensionality from parallel analysis, VSS and MAP, and very good fits to the 1-factor CFA model with CFI, TLI values all >0.97 (COSMIN criteria). MGCFA indicated different country translations of the DLQI conceptualize the same construct, are all unidimensional with equality of factor loadings. Known-group analysis of DLQI versus disease severity and versus EQ-5D VAS quartiles were significant for every country (all p<0.025).
CONCLUSIONS: Excellent psychometric properties were present across all 13 languages examined. Unidimensionality of the DLQI construct was confirmed and the DLQI is able to differentiate between levels of disease severity and EQ-5D levels across all these languages. This adds further confidence in the appropriateness of using the DLQI across this range of languages.
Conference/Value in Health Info
2025-11, ISPOR Europe 2025, Glasgow, Scotland
Value in Health, Volume 28, Issue S2
Code
PCR77
Topic
Clinical Outcomes, Methodological & Statistical Research, Patient-Centered Research
Topic Subcategory
Instrument Development, Validation, & Translation
Disease
Biologics & Biosimilars, Sensory System Disorders (Ear, Eye, Dental, Skin), Systemic Disorders/Conditions (Anesthesia, Auto-Immune Disorders (n.e.c.), Hematological Disorders (non-oncologic), Pain)