Reciprocal causation between functional independence and mental health 1 and 2 years after traumatic brain injury: A cross-lagged panel structural equation model

Objective: The research attempting to disentangle the directionality of relationships between mental health and functional outcomes after traumatic brain injury (TBI) is growing but has yielded equivocal findings or focused on isolated predictors or isolated outcomes. The purpose of the current study was to use cross-lagged panel and structural equation modeling (SEM) techniques to examine causality between comprehensive indices of mental health (depression, anxiety, and life satisfaction) and functional independence in a national sample of individuals with TBI over the first 2 years after injury. Design: Participants were 4,674 individuals with TBI from the TBI Model Systems Database. Results: The SEM, which yielded good fit indices, suggested that individuals with TBI with greater mental health problems at 1 and 2 years after injury had lower functional independence at those same time points. The standardized path loadings for mental health problems and for functional independence over time were large, suggesting a high degree of consistency in mental health and functional independence across 1 and 2 years. In terms of cross-lag, mental health at Time 1 did not exert a unique effect on functional independence at Time 2, but functional independence at Time 1 exerted a statistically significant but quite small unique effect on mental health at Time 2. Conclusions: This combination of results suggests that functional independence is only slightly more causal than mental health in the relationship between mental health and functional independence over the first 2 years post-TBI, and that instead, reciprocal causality is a more likely scenario.