The impact of vision impairment questionnaire: An evaluation of its measurement properties using Rasch analysis

Abstract

PURPOSE. To explore the psychometric properties of the Impact of Vision Impairment scale (IVI) by using Rasch analysis. METHODS. Three hundred fourteen first-time referrals to low-vision clinics completed the 32-item IVI. The data were Rasch-analyzed with a partial credit model using RUMM2020 software (RUMM Laboratory, Perth, WA, Australia). The overall fit of the model, response scale, individual item fit, differential item functioning, unidimensionality, and person-separation reliability were assessed. RESULTS. Initially, 26 items displayed disordered thresholds. However, collapsing the response scale to three categories (4 items) and four categories (28 items) produced ordered response th..