Equating Visual Function Scales to Facilitate Reporting of Medicare Functional G-Code Severity/Complexity Modifiers...

Area of Science:

• Ophthalmology
• Rehabilitation Medicine
• Health Services Research

Background:

• Comparing functional status across different visual function questionnaires (VFQs) is challenging due to varied scales.
• Standardizing these measures is crucial for accurate patient assessment and effective healthcare management, particularly for Medicare G-code severity modifiers.

Purpose of the Study:

• To develop and present a method for estimating and equating scales across various functional assessment instruments.
• To ensure that changes in patient functional ability are accurately represented and can be meaningfully mapped to Medicare G-code severity modifiers.

Main Methods:

• Equated previously published visual ability measures from 7 different VFQs using Rasch analysis.
• Mapped these equated scales onto Medicare G-code severity modifiers.
• Utilized bivariate regression and logistic functions to transform VFQ item measures to a common scale.

Main Results:

• Developed a method to linearly transform Self-Report Assessment of Functional Visual Performance (SRAFVP) and Veterans Affairs Low Vision Visual Functioning Questionnaire (VA LV VFQ) item measures to the Activity Inventory (AI) scale.
• Estimated regression coefficients for 7 VFQs to approximate the nonlinear relationship between visual ability measures and raw scores.
• Demonstrated the ability to estimate functional ability on a common interval scale and transform VFQ responses to Medicare G-code categories.

Conclusions:

• Equated interval scales facilitate comparison of functional status and outcomes across different measurement instruments for low-vision patients.
• The presented method is applicable to any area of rehabilitation, promoting standardized outcome measurement.