Skindex, a quality-of-life measure for patients with skin disease: reliability, validity, and responsiveness

Abstract

To measure the effects of skin disease on patients' quality of life, we developed a 61-item self-administered survey instrument called Skindex. Skindex has eight scales, each of which addresses a construct, or an abstract component, in a comprehensive conceptual framework: cognitive effects, social effects, depression, fear, embarrassment, anger, physical discomfort, and physical limitations. Item responses are standardized from 0 (no effect) to 100 (maximal effect); a scale score is the average of responses to items addressing a construct. In 201 patients seen by dermatologists, mean scale scores (+/-SD) ranged from 14 (+/-17) for physical limitations to 31 (+/-22) for physical discomfort. Scale scores were reproducible after 72 h (r = 0.68-0.90) and were internally consistent (Cronbach's alpha = 0.76-0.86). Construct validity was assessed in two ways: (i) in a comparison of patients with inflammatory dermatoses and patients with isolated lesions, patients with inflammatory dermatoses had higher scale scores, and (ii) in an exploratory factor analysis, 78% of the common variance was explained by seven factors that correlated with the scale scores of Skindex. Most of the a priori scale scores changed in the expected direction in patients who reported that their skin conditions had improved or worsened after 6 mo. Finally, physicians' judgments of disease severity did not consistently correlate with Skindex scores. These preliminary data suggest that Skindex reliably and responsively measures the effects of skin disease on patients' quality of life and may supplement clinical judgments of disease severity.