LAUSR

OBJECTIVE To investigate relative causality in relations among suicidal ideation (SI), depressive symptoms, and functional independence over the first 10 years after traumatic brain injury (TBI). DESIGN Prospective longitudinal design with data collected through the TBI Model Systems (TBIMS) network at acute rehabilitation hospitalization, as well as 1, 2, 5, and 10 years after injury. SETTING United States Level I/II trauma centers and inpatient rehabilitation centers with telephone follow-up. PARTICIPANTS Individuals enrolled into the TBIMS National Database (N=9539) with at least one SI score at any follow-up data collection (72.1% male, mean age = 39.39 years). INTERVENTIONS Not applicable. MAIN OUTCOME MEASURE Patient Health Questionnaire-9 and Functional Independence Measure at years 1, 2, 5, and 10 post-injury. RESULTS A cross-lagged panel structural equation model (SEM), which is meant to indirectly infer causality through longitudinal correlational data, suggested that SI, depressive symptoms, and functional independence each significantly predicted themselves over time. Within the model, bivariate correlations among variables were all significant within each time point. Between years 1 and 2 and between years 2 and 5, depressive symptoms had a larger effect on SI than SI had on depressive symptoms. Between years 5 and 10, there was reciprocal causality between the two variables. Functional independence more strongly predicted depressive symptoms than the reverse between years 1 and 2 as well as years 2 and 5, but its unique effects on SI over time were extremely marginal or absent after controlling for depressive symptoms. CONCLUSIONS A primary goal for rehabilitation and mental health providers should be to monitor and address elevated symptoms of depression as quickly as possible before they translate into SI, particularly for individuals with TBI who have reduced functional independence. Doing so may be a key to breaking the connection between low functional independence and SI.