Criterion validity of the Delis-Kaplan Executive Function System (D-KEFS) fluency subtests after traumatic brain injury.

The performance of 65 patients with complicated mild-severe traumatic brain injury was evaluated on the Verbal and Design Fluency subtests of the Delis-Kaplan Executive Function System (D-KEFS), and compared with that of 65 demographically matched healthy controls. There were statistically significant group differences on Letter Fluency and Category Switching but not on any of the Design Fluency tasks. Combined, these two Verbal Fluency subtests had a classification accuracy of 65.39%, associated with a likelihood ratio of 1.87. The impact of length of coma on Letter Fluency performance but not Category Switching was mediated at least in part by processing speed. The findings suggest modest criterion validity of some of the D-KEFS Verbal Fluency subtests in the assessment of patients with complicated mild-severe traumatic brain injury.