Refinement and validation of the ItchyQoL using classical test theory and item response theory resulted in a reduction of the response categories from a 5?point to a 3?point scale

The ItchyQoL is an itch?specific patient?reported outcome measure used to assess quality of life in patients with chronic pruritus (CP). We aimed and extend the psychometric properties using classical test theory (CTT) item response (IRT). Item characteristic curves were analysed investigate whether categories functioning optimally. Confirmatory factor analyses carried out on prior after rescoring categories. conducted a Rasch analysis for revised options assessed mean fit residuals addition assumptions unidimensionality local independence. In total, 551 CP from nine European countries completed 22 items ItchyQoL. IRT supported revision five points three. This was by excellent structural validity CTT. overall model adequate. Unidimensionality scale single subscales; however, independence violated eight cases. suggest 5?point 3?point scale. When this applied, showed according CTT IRT/Rasch. calculation sum score allowed.