[Item response theory and its application in neurology. Measurement of activity limitations in neurologic patients]

This article is concerned with the measurement of activity limitations in neurologic patients and with the application of the item response theory (IRT), especially the Rasch analysis, in analyzing activity ratings. Activity limitations of 166 patients with different neurologic disorders (e.g., stroke, traumatic brain injury) were assessed with the Functional Independence Measure (FIM) during their stay in a rehabilitation hospital. Data analysis was performed with the Rasch model, which allows testing the psychometric qualities of the FIM. Results indicate that the FIM has good psychometric qualities. However, results also show that the 18 FIM items define two statistically and clinically different indicators. Thirteen items define disability in motor functions. Five items define disability in cognitive functions. Separate analyses of the two scales help to improve the psychometric quality of the FIM.