The effects of intelligence on exposure to combat and posttraumatic stress disorder across multiple deployments

Introduction: Past work relates intelligence quotient (IQ) to risk for Post-Traumatic Stress Disorder (PTSD) among soldiers. We gathered data over multiple deployments to assess how IQ relates to the rate of symptom development both directly and through increasing the risk for traumatic combat exposure. Methods: Male infantry soldiers from a maneuver brigade (N = 582) were followed over the 3-year period of their mandatory military service. Data were collected at 3-time-points: 1) shortly after enlistment and before deployment; 2) about 15 months into the service following one deployment, and another year later following additional deployments. IQ was measured before recruitment into the military; PTSD symptoms and combat exposure were measured at each time-point. Results: Lower general IQ, and in particular lower abstract reasoning capabilities, related to steeper increases in PTSD symptoms, TIME×IQ= -.05, SE= .02, t(442.79) = -3.255, p < .01, controlling for the effect of pre-military traumatic experience. This relation was partly mediated by combat exposure, Effect= -.04, BootSE= .01, 95 % CI [-.06, −.02]. Conclusion: The results identify important risk factors for PTSD that can inform approaches to PTSD mitigation in the military and other organizations. Given that this study enrolled a male sample the generalizability of the results awaits further research.