Calibration of the Activity Inventory Item Bank: A Patient-Reported Outcome Measurement Instrument for Low Vision Rehabilitation.

Purpose: To provide calibrated item measures and rating category thresholds for the Activity Inventory (AI), an adaptive visual function questionnaire, from difficulty ratings obtained from a large sample of new low vision patients at pre-rehabilitation baseline. Methods: Baseline AI (510 items) rating scale data from five previous low vision rehabilitation outcome studies (n = 3623) were combined, and the method of successive dichotomizations was used to estimate calibrated item measures and rating category thresholds. Infit statistics were analyzed to evaluate the fit of the data to the model. Factor analysis was applied to person measures estimated from different subsets of items (e.g., functional domains such as reading, mobility) to evaluate differential person functioning. Results: Estimated item measures were well targeted to the low vision patient population. The distribution of infit statistics confirmed the validity of the estimated measures and the two-factor structure previously observed for the AI. Conclusions: Our calibrated item measures and rating category thresholds enable researchers to estimate changes in visual ability from low vision rehabilitation on the same scale, facilitating comparisons between studies. Translational Relevance: The work described in this paper provides calibrated item measures and rating category thresholds for a visual function questionnaire to measure patient-centered outcomes in low vision clinical research. The calibrated AI also can be used as a patient outcome measure and quality assurance tool in clinical practice.