Effect of Dwell Time on the Mental Health of US Military Personnel With Multiple Combat Tours

Objective: We investigated the association of the length of time spent at home between deployments, or dwell time, with posttraumatic stress disorder (PTSD) and other mental health disorders. Methods: We included US Marine Corps personnel identified from military deployment records who deployed to Operation Iraqi Freedom once (n = 49 328) or twice (n = 16 376). New-onset mental health diagnoses from military medical databases were included. We calculated the ratio of dwell-to-deployment time (DDR) as the length of time between deployments divided by the length of the first deployment. Results: Marines with 2 deployments had higher rates of PTSD than did those with 1 deployment (2.1% versus 1.2%; P < .001). A DDR representing longer dwell times at home relative to first deployment length was associated with reduced odds of PTSD (odds ratio [OR] = 0.47; 95% confidence interval [CI] = 0.32, 0.70), PTSD with other mental health disorder (OR = 0.56; 95% CI = 0.33, 0.94), and other mental health disorders (OR = 0.62; 95% CI = 0.51, 0.75). Conclusions: Longer dwell times may reduce postdeployment risk of PTSD and other mental health disorders. Future research should focus on the role of dwell time in adverse health outcomes.