Taking a closer look at the Cognitive Scale of the Functional Independence Measure and its clinical application in severe traumatic brain injury: A psychometric study

Despite widespread use of the Functional Independence Measure (FIM) in clinical and research settings, the applicability of the Cognitive scale to the traumatic brain injury (TBI) group remains problematic. This study evaluated the clinical utility of the FIM-Cognitive scale. We examined the sensitivity, specificity, and positive and negative predictive values of the five items of the FIM-Cognitive scale, by comparing them with reference standards provided by performance on 14 specific cognitive and behavioural variables that mapped to individual FIM-Cognitive items. A total of 67 participants with severe TBI comprised an Inpatient sample (n = 35), assessed at 2- and 6-months post-trauma, and a Community sample (n = 32) at 3-years post-trauma. Ceiling effects were common and high (>20% on 14/15 FIM-Cognitive items from Inpatient and Community samples), which impacted responsiveness. Sensitivity, specificity, positive and negative predictive values were highly variable in all samples, but few reached an 80% threshold on any index. The clinical utility of the FIM-Cognitive scale thus has significant limitations when used with the severe TBI group, both in the post-acute stages and longer-term. These results suggest that the FIM-Cognitive scale should not be used in isolation for clinical decision-making purposes or benchmarking and service delivery.