The functional assessment measure (FAM) in closed traumatic brain injury outpatients: a Rasch-based psychometric study

The Functional Assessment Measure (FAM) has been proposed as a measure of disability in post-acute Traumatic Brain Injury (TBI) outpatients. It is comprised of the 18 items of The Functional Independence Measure (FIMSM), scored in terms of dependence, and of 12 newly designed items, scored in terms of dependence (7 items) or performance (5 items). The FIMSM covers the domains of self-care, sphincter management, mobility, locomotion, communication and social cognition. The 12 new items explore the domains of community integration, emotional status, orientation, attention, reading/writing skills, swallowing and speech intelligibility. By addressing a set of problems quite specific for TBI outpatients the FAM was intended to raise the ceiling of the FIMSM and to allow a more precise estimate of their disability. These claims, however, were never supported in previous studies. We administered the FAM to 60 TBI outpatient, 2-88 months (median 16) from trauma. Rasch analysis (rating scale model) was adopted to test the psychometric properties of the scale. The FAM was reliable (Rasch item and person reliability 0.91 and 0.93, respectively). Two of the 12 FAM-specific items were severely misfitting with the general construct, and were deleted. Within the 28-item refined FAM scale, 4 new items and 2 FIMSM items still retained signs of misfit. The FAM was on average too easy. The most difficult item (a new one, Employability) did not attain the average ability of the subjects. Also, it was only slightly more difficult than than the most difficult FIMSM item (Memory). The FAM does not seem to improve the FIMSM as a far as TBI outpatients are to be assessed.