Reliability and validity of the psoriasis symptom inventory in patients with moderate-to-severe psoriasis

Objectives: The psoriasis symptom inventory (PSI) is a patient-reported outcome measure for assessing symptom severity in patients with moderate-to-severe psoriasis. The primary objective of this study was to evaluate the measurement properties of the PSI. Materials and methods: Analyses of psychometric characteristics (reliability, convergent and known-groups validity,responsiveness, item performance, and dimensionality) were conducted using data from a Phase II trail to evaluate efficacy of brodalumab in subjects with moderate–to-severe psoriasis. Results: The PSI had excellent internal consistency (α = 0.93–0.98) and good test-retest reliability (ICCs = 0.77–0.87). Convergent and discriminant validity was indicated by moderate-to-strong correlations between the PSI and Dermatology Life Quality Index scores, and small correlations between PSI total scores and ShortfFrm-36 Health Survey mental health, role emotional, and role physical scales. Known groups validity was shown as mean PSI total scores varie...