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Cross-diagnostic validity in a generic instrument: an example from the Functional Independence Measure in
A Lundgren-Nilsson1, A Tennant, G Grimby
1Sahlgrenska Academy at Göteborg University, Institute of Neuroscience and Physiology/Rehabilitation medicine, Guldhedsgatan 19 413 45 Göteborg, Sweden. asa.lundgren-nilsson@rehab.gu.se
Health and Quality of Life Outcomes
|August 25, 2006
Summary
The Functional Independence Measure (FIM) motor items require adjustments for cross-diagnostic validity in spinal cord injury, stroke, and traumatic brain injury patients. Rescoring and item removal improve FIM scale validity for comparing patient outcomes.
Area of Science:
- Rehabilitation medicine
- Psychometrics
- Clinical assessment
Background:
- The Functional Independence Measure (FIM) is widely used in rehabilitation.
- Its cross-diagnostic validity and score comparability across different neurological conditions are not fully established.
- Spinal cord injury (SCI), stroke, and traumatic brain injury (TBI) populations present unique challenges for assessment.
Purpose of the Study:
- To analyze the cross-diagnostic validity of FIM motor items in SCI, stroke, and TBI patients.
- To assess the comparability of summed FIM motor scores between these diagnostic groups.
- To evaluate the suitability of the FIM's seven-category scoring system using Rasch modeling.
Main Methods:
- Rasch modeling was applied to FIM motor item data from 471 patients (157 each of SCI, stroke, TBI).
- Scoring functions were analyzed and categories rescored to improve model fit.
- Differential Item Functioning (DIF) and Test Equating were used to assess cross-diagnostic comparability.
Main Results:
- The original seven-category scoring system for FIM motor items was found invalid, necessitating rescoring.
- Two items (Eating, Bladder management) showed misfit to the Rasch model.
- Significant cross-diagnostic DIF was detected, particularly for SCI, but score comparability was achieved after adjustments.
Conclusions:
- The seven-category response function of the FIM instrument poses validity challenges.
- Reducing response categories and removing misfit items could enhance FIM scale validity.
- While cross-diagnostic DIF is a concern, adjusted sum scores on group data allow for clinical comparisons of the FIM in diverse patient populations.
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