Measurement properties of three assessments of burden used in atopic dermatitis in adults.

BACKGROUND: Standardized quality-of-life (QoL) assessments can provide important and clinically relevant information. There is currently a lack of standardization in QoL assessments used in atopic dermatitis (AD). OBJECTIVES: To determine the content validity, construct validity, internal consistency, differential reporting, responsiveness, floor or ceiling effects and feasibility of the Dermatology Life Quality Index (DLQI), Itchy Quality of Life (ItchyQoL) and 5-dimensions (5-D) itch scales for assessing burden of AD in adults and to compare their performance. METHODS: Self-administered questionnaires and skin examination were performed in 340 adults with AD in a dermatology practice setting. RESULTS: DLQI, ItchyQoL and 5-D all had good content validity. DLQI, mean ItchyQoL and 5-D itch all had strong correlations with frequency of AD symptoms (Patient-Oriented Eczema Measure) and intensity of itch (numerical rating scale for itch), and moderate correlations with AD severity (Eczema Area and Severity Index and Scoring Atopic Dermatitis) (Spearman correlations, P < 0·001 for all). DLQI and 5-D itch showed good internal consistency (Cronbach's alpha = 0·89 and 0·84), although ItchyQoL appeared to have several redundant items (alpha = 0·96). Uniform and nonuniform differential item functioning by age, sex and/or race/ethnicity was found for multiple items in DLQI, ItchyQoL and 5-D itch. DLQI, ItchyQoL and 5-D itch scores all demonstrated responsiveness, although ItchyQoL demonstrated the greatest responsiveness. There were no floor or ceiling effects for total scores. The median times for completion of DLQI, ItchyQoL and 5-D itch were 2 min. CONCLUSIONS: The DLQI, ItchyQoL and 5-D itch scales all showed good content and construct validity, and responsiveness in the assessment of AD in adults, and were feasible for use in clinical trials and practice.