Objective: The purpose of this study was to examine rate and pattern of change in executive functioning as measured by the Symbol Digit Modalities Test (SDMT) in patients recovering from Traumatic Brain Injury (TBI). Hanks et al. (1999) found that executive functioning predicted functional outcome at 6 month in TBI patients. Method: Neuropsychological and demographic data of 16172 individuals with TBI were obtained from the TBI Model Systems National Database and Archived Collaborative Module Study Databases. To account for the nested nature of the data (three timepoints nested in individuals), multilevel modeling was employed. To examine change in SDMT performance, the fixed effects of time, injury severity (mild, moderate, and severe), and education were added as predictors in successive models. Results: The first model revealed a linear rate of SDMT score improvement over time (b = 3.297, 95%CI [2.485, 4.11]). Results of the second model suggest that that rate of improvement depends on injury severity (t (1423.13) = 2.85, 95% CI [.42, 2.26]); more severe injury resulted in lower SDMT scores (b = −1.02, 95%CI [−1.89, −.16]). The third model demonstrated that education effects improvement over time, such that higher education was associated with better SDMT scores (b = 1.06, 95%CI [.64, 1.47]). Overall, the third model, which included level of education, predicted recovery of SDMT performance better than the model containing injury severity only (χ2 difference (726.75)= 5896.67, p < .05). Conclusion: Pre-injury level of education significantly predicts recovery of executive functioning after TBI irrespective head injury severity.

graphic