Development, Validation, and Interpretation of the PROMIS Itch Questionnaire: A Patient-Reported Outcome Measure for the Quality of Life Impact of Itch

Abstract

Current patient-reported outcome measures for itch are limited and may not capture its full impact on health-related quality of life. We sought to develop, calibrate, and validate banks of questions assessing the health-related quality of life impact of itch as part of the Patient-Reported Outcomes Measurement Information System. A systematic process of literature review, content-expert review, qualitative research, testing in a sample of 600 adults, classical test theory methods, and item response theory analyses were applied. Exploratory and confirmatory factor analyses were followed by item response theory model and item fit analyses. Four itch-related item banks were developed: (i) general concerns, (ii) mood and sleep, (iii) clothing and physical activity, and (iv) scratching behavior. Item response theory and expert content review narrowed the item banks to 25, 18, 15, and 5 items, respectively. Validity of the item banks was supported by good convergent and discriminant validity with itch intensity, internal consistency, and no significant floor or ceiling effects. In conclusion, the Patient-Reported Outcomes Measurement Information System Itch Questionnaire banks have excellent measurement properties and efficiently and comprehensively assess the burden of itch.