Calibration of clinical and self-report measures in blind rehabilitation
 
JL Babcock, Ph.D1., DN Head, Ed.D1, PE McKnight, Ph.D.2, R Massof, Ph.D.3
 
1Southern AZ VA Health Care System, 2University of Arizona, Lions Vision Research and Rehabilitation Center, 3Wilmer Ophthalmological Institute, Johns Hopkins University
 
Objectives: The primary purpose of this project is to calibrate two outcome instruments used to measure functional ability in geriatric patients who are blind or severely visually impaired. Calibration of the two measures permits easy transformations of values in order to establish a "gold standard" to be used for benchmarking blind rehabilitation outcomes across VA Blind Rehabilitation Centers and to exam alternative service delivery models. The two measures calibrated are the Blind Rehabilitation Service Follow-up Outcome Survey (BRSFOutSur) and the Functional Assessment of Self-reliance on Tasks (FAST). The BRSFOutSur is a self-report instrument developed and administered over the past three years by researchers at the Atlanta RR&D Center. The FAST is a clinical measure of functional ability and was developed during the same time period by researchers at Southwestern Blind Rehabilitation Center (SWBRC).
 
Methods: The BRSFOutSur data were collected 3-months post-discharge (i.e., retrospective pretest and posttest) through a phone survey and the FAST data were collected at admission and discharge. Both measures sampled veterans who attended the inpatient blind rehabilitation program at SWBRC. The two databases were merged yielding approximately 300 matching cases for the secondary analyses. In order to develop a common measurement metric, Rasch analyses were conducted to estimate the difficulty of the survey items. Subsequent to the Rasch analysis, a generalizability study was used to identify sources of variation and under what circumstances survey responses are meaningful. Following these procedures, both Rasch score matching as well as classical raw score bivariate regression analyses were performed to compute and algebraic formula for converting scores from the BRSFOutSur to the FAST and vice versa.
 
Results: The Rasch analyses provided information about the stability of items both within a single assessment period and over two separate assessment periods (i.e., pre- and post). From these results, only those items that performed well were kept for the calibration procedures. An algebraic conversion algorithm was determined and the implications and their use are discussed in detail. The analyses also identified the personal characteristics that moderate change (e.g., eye disease, acuity, and health comorbities) and item characteristics (e.g., item difficulty, interval stability, assessing tasks versus goals). From these findings, the development of a patient profiling system will lead to the establishment of defensible benchmarks that will set standards of expectation for improvement in veterans’ functional abilities following blind rehabilitation training.
 
Conclusions: The calibration methods employed in this study have identified functional ability items that can be used interchangeably. These items can also be used as benchmarks to identify a program’s effectiveness. Further development of these calibration methods should provide the basis for developing a common measurement metric with which to determine functional improvement. These findings also provide a foundation for understanding measurement theory in low vision rehabilitation.
 
Funding Acknowledgment: This study was funded by the VA Rehabilitation Research and Development Service, project #C-2710I.