Early development and qualitative evidence of content validity for the Psoriasis Symptom Inventory (PSI), a patient-reported outcome measure of psoriasis symptom severity

Objective: To develop and assess content validity of the Psoriasis Symptom Inventory (PSI), a patient-reported outcome (PRO) measure of psoriasis symptoms. Methods: Following initial literature exploration and input from experts, concept elicitation was conducted in two rounds (focus groups and individual interviews) with 59 subjects with mild to severe psoriasis. Transcripts were coded to identify symptom concepts and develop a conceptual framework using ATLAS.ti software. Qualitative content analysis and clinical expert input supported item generation and development of a draft measure. Two rounds of face-to-face cognitive interviews with 40 subjects with moderate to severe psoriasis were conducted to test subject comprehension and content coverage. Results: Concepts of itching, scaling, flaking, tearing/cracking, burning, stinging, pain, bleeding and color of appearance were the most common symptom-related expressions. Saturation of concept was demonstrated. Severity was identified as the most meaningful attribute of psoriasis symptoms. A final 8-item measure was developed to assess patient-perceived symptom severity for itch, pain, burning, stinging, cracking, scaling, flaking and redness. Twenty-four-hour recall and 7-day recall versions were prepared for future quantitative assessment of measurement properties. Conclusions: The PSI is a short, low burden, patient-reported measure of psoriasis symptom severity with documented evidence of content validity.