Objective: The Functional Independence Measure (FIM) is an internationally widely used outcome measure. The aim of this study was to evaluate the structural properties of FIM using the Rasch model, with regard to scoring within rehabilitation centres in Scandinavia.
Materials and methods: FIM data from 1660 patients with stroke, traumatic brain injury and spinal cord injury were analysed. The best models with respect to person separation were determined, together with person reliability, item separation, disordered categories, distance of more than 1.4 logits between categories and item fit to the model.
Results: Analysis showed disordering using seven categories in all three diagnoses. After collapsing of categories a four-category scale was the best solution.
Conclusions: Decreasing the categories from seven to four may be one way of dealing with problems of disordered thresholds. Further studies are also needed in order to try the suggested scale in clinical settings and to compare it with the original FIM scale.