Luther SL (VISN 8 Patient Safety Research Center)
Powell-Cope G (VISN 8 Patient Safety Research Center)
Kromrey J (University of South Florida)
Rosenberg D (VISN 8 Measurement Evaluation Team)
Nelson A (VISN 8 Patient Safety Research Center)
Quigley P (VISN 8 Patient Safety Research Center)
Several items on the SF-36 Physical Functioning (PF) scale are worded inappropriately (i.e. "Climbing one flight of steps") for persons with SCI. The purpose of this study was to modify the SF-36V Physical Functioning (PF) Scale for use with Spinal Cord Injured veterans.
Focus groups were conducted with veterans with SCI and their caregivers to identify alternative wording for SF-36 PF items. An attempt was made to maintain the structure of the original PF items as closely a possible. In addition to the re-worded PF items additional items of physical functioning, adapted from Haley’s Late Life Function and Disability Instrument, were also included. The pool of items was then included in a written questionnaire with the other components SF-36 items, and information about activities of daily living, level of injury, physical functioning, and demographics. After pilot testing the questionnaire was mailed to all persons with SCI who have the at the Tampa VA SCI Center as their medical provider (n=787).
A total of 392 usable questionnaires were obtained (response rate = 49.8%). Exploratory factors analysis suggested that the revised items involving mobility did not represent a uni-dimensional construct in both paraplegic and tetraplegic respondents. However, a brief set (7) of items, including several reworded original SF-36 items, was identified that did have a similar factor structure in both SCI groups. Item Response Theory (Rausch) models items were developed to determine item parameters for the new scale. Tests of differential item functioning found the scale worked well with both paraplegic and tetraplegic respondents. Support for convergent and divergent validity of the resultant scales are described.
These results suggest that, even after rewording, the original SF-36 PF are not valid in both paraplegic and tetraplegic SCI patients. However, we describe a brief set of PF items that place more emphasis on freedom and independence in this population.
The SF-36 questionnaire is used widely in the VA. Results of this study suggest that using the traditional PF scale with SCI patients could lead to biased results. The alternative scale reported in the current study should be considered as an alternative.