What do Vitiligo Impact Scale-22 scores mean? Studying the clinical interpretation of scores using an anchor-based approach.

ABSTRACT

BACKGROUND: The Vitiligo Impact Scale (VIS)-22 is a vitiligo-specific quality-of-life instrument. Its criterion, convergent and known-groups validity, test-retest reliability and responsiveness have been studied previously in an Indian population. The clinical meaning of VIS-22 scores has not yet been analysed. OBJECTIVES: To assign clinical meaning to VIS-22 scores using anchor-based methods. METHODS: This was a cross-sectional study conducted in a large teaching hospital in North India. Patients with vitiligo > 15 years of age (n = 391) completed the VIS-22 and Dermatology Life Quality Index (DLQI) questionnaires, and answered a Global Question (GQ) on the effect of vitiligo on their lives on a five-point Likert scale. Multiple band sets of VIS-22 scores were devised using GQ as the anchor. A weighted kappa-coefficient was calculated to estimate the level of agreement between different band sets of VIS-22 and GQ. VIS-22 and DLQI were compared based on their degree of correlation and agreement with GQ. RESULTS: The mean ± SD of VIS-22 scores was 24·8 ± 14·0 (range 0-61). VIS-22 scores showed good correlation with GQ (r = 0·76). Of the various VIS-22 band sets tested, the following was chosen 0-5, 6-15, 16-25, 26-40 and 41-66 (weighted κ = 0·57), corresponding to the five categories of GQ. The degree of correlation (VIS-22, r = 0·77; DLQI, r = 0·69) and agreement (VIS-22, 51·6%; DLQI, 36·1%; P < 0·001) of VIS-22 with GQ was higher than that with DLQI. CONCLUSIONS: VIS-22 scores can be used to stratify the impairment of vitiligo-related quality of life.