Calibrating the impact of vision impairment (IVI): Creation of a sample-independent visual function measure for patient-centered outcomes research

Abstract

Purpose: Provide item calibrations estimated for the Impact of Vision Impairment (IVI) questionnaire by pooling data from several studies of people with vision impairment (VI) representing a variety of countries and causes of VI. Methods: Eight data sets from six principal investigators representing responses to IVI items from 2867 VI patients were pooled for analysis. Eligible patients were 18 years or older and from Australia, India, and the United States. Rasch analysis, using the Andrich Rating Scale Model (Winsteps version 3.65), was performed on preinterven-tion IVI responses to estimate item and person measures, reliability coefficients, and response category thresholds. Differential ..