Article

OBJECTIVE: To present a method of estimating and equating scales across
functional assessment instruments that appropriately represents changes in a
patient's functional ability and can be meaningfully mapped to changes in
Medicare G-code severity modifiers. DESIGN: Previously published measures of
patients' overall visual ability, estimated from low-vision patient responses to
7 different visual function rating scale questionnaires, are equated and mapped
onto Medicare G-code severity modifiers. SETTING: Outpatient low-vision
rehabilitation clinics. PARTICIPANTS: The analyses presented in this article were
performed on raw or summarized low-vision patient ratings of visual function
questionnaire (VFQ) items obtained from previously published research studies.
INTERVENTIONS: Previously published visual ability measures from Rasch analysis
of low-vision patient ratings of items in different VFQs (National Eye Institute
Visual Functioning Questionnaire, Index of Visual Functioning, Activities of
Daily Vision Scale, Visual Activities Questionnaire) were equated with the
Activity Inventory (AI) scale. The 39 items in the Self-Report Assessment of
Functional Visual Performance (SRAFVP) and the 48 items in the Veterans Affairs
Low Vision Visual Functioning Questionnaire (VA LV VFQ) were paired with similar
items in the AI in order to equate the scales. MAIN OUTCOME MEASURES: Tests using
different observation methods and indicators cannot be directly compared on the
same scale. All test results would have to be transformed to measures of the same
functional ability variable on a common scale as described here, before a single
measure could be estimated from the multiple measures. RESULTS: Bivariate
regression analysis was performed to linearly transform the SRAFVP and VA LV VFQ
item measures to the AI item measure scale. The nonlinear relationship between
person measures of visual ability on a logit scale and item response raw scores
was approximated with a logistic function, and the 2 regression coefficients were
estimated for each of the 7 VFQs. These coefficients can be used with the
logistic function to estimate functional ability on the same interval scale for
each VFQ and for transforming raw VFQ responses to Medicare's G-code severity
modifier categories. CONCLUSIONS: The principle of using equated interval scales
allows for comparison across measurement instruments of low-vision functional
status and outcomes, but can be applied to any area of rehabilitation.
CI - Copyright (c) 2015 American Congress of Rehabilitation Medicine. Published by
Elsevier Inc. All rights reserved.

Langue : ANGLAIS