Rasch analysis of the UK Functional Assessment Measure in patients with complex disability after stroke
Oleg N. Medvedev, Lynne Turner-Stokes, Stephen Ashford, Richard J. Siegert
Centre of Medical and Health Sciences Education, Auckland University of Technology, 0626 North Shore, 1142 Auckland, New Zealand. E-mail: firstname.lastname@example.org
Objectives: To determine whether the UK Functional Assessment Measure (UK FIM+FAM) fits the Rasch model in stroke patients with complex disability and, if so, to derive a conversion table of Rasch-transformed interval level scores.
Methods: The sample included a UK multicentre cohort of 1,318 patients admitted for specialist rehabilitation following a stroke. Rasch analysis was conducted for the 30-item scale including 3 domains of items measuring physical, communication and psychosocial functions. The fit of items to the Rasch model was examined using 3 different analytical approaches referred to as ”pathways”.
Results: The best fit was achieved in the pathway where responses from motor, communication and psychosocial domains were summarized into 3 super-items and where some items were split because of differential item functioning (DIF) relative to left and right hemisphere location (χ2 (10) = 14.48, p = 0.15). Re-scoring of items showing disordered thresholds did not significantly improve the overall model fit.
Conclusion: The UK FIM+FAM with domain super-items satisfies expectations of the unidimensional Rasch model without the need for re-scoring. A conversion table was produced to convert the total scale scores into interval-level data based on person estimates of the Rasch model. The clinical benefits of interval-transformed scores require further evaluation.
Functionality of patients after stroke is difficult to assess accurately because of differences between physical, communication and psychosocial functions. This study employed statistical method called Rasch analysis to evaluate the UK Functional Assessment Measure (UK FIM+FAM) using assessments results of 1318 stroke patients. We found that the UK FIM+FAM is a good measure of global functionality that includes physical, communication and psychosocial aspects without the need for modifications. We produced statistically adjusted assessment scores to improve accuracy of the UK FIM+FAM assessments but clinical benefits of such adjustments require further evaluation.