Prospective post-traumatic stress disorder symptom trajectories in active duty and separated military personnel). LGMM esti-mates latent classes containing different growth trajectories that

Abstract

Post-traumatic stress disorder (PTSD) is a serious mental illness that affects current and former military service members at a disproportionately higher rate than the civilian population. Prior studies have shown that PTSD symptoms follow multiple trajectories in civilians and military personnel. The current study examines whether the trajectories of PTSD symptoms of veterans separated from the military are similar to continuously serving military personnel. The Millennium Cohort Study is a population-based study of military service members that commenced in 2001 with follow-up assessments occurring approximately every 3 years thereafter. PTSD symptoms were assessed at each time point using the PTSD Checklist. Latent growth mixture modeling was used to compare PTSD symptom trajectories between personnel who separated (veterans; n ¼ 5292) and personnel who remained in military service (active duty; n ¼ 16,788). Four distinct classes (resilient, delayed-onset, improving, and elevated-recovering) described PTSD symptoms trajectories in both veterans and active duty personnel. Trajectory shapes were qualitatively similar between active duty and veterans. However, within the resilient, improving, and elevated recovering classes, the shapes were statistically different. Although the low-symptom class was the most common in both groups (veterans: 82%; active duty: 87%), veterans were more likely to be classified in the other three classes (in all cases, p < 0.01). The shape of each trajectory was highly similar between the two groups despite differences in military and civilian life. Military personnel are often exposed to traumatic events while deployed in support of conflicts (Castro and McGurk, 2007; Hoge et al., 2004). Consequently, post-traumatic stress disorder (PTSD) is a significant health concern of current and former military service members (Hoge et al., 2004, 2006; Smith et al., 2008). A substantial proportion of combat-related PTSD research is conducted within the Department of Defense, examining current service members, and within the Department of Veteran Affairs (VA), examining veterans. However, research has demonstrated incon-gruent results in these populations. For example, studies report more prevalent PTSD among veterans than current service members (Dursa et al., 2014; Ramchand et al., 2010). Estimates of PTSD prevalence in current military personnel deployed in support of Operation Enduring Freedom/Operation Iraqi Freedom (OEF/OIF) were 7% in 2005 and 11% in 2008 (Bray et al., 2010). In contrast, between 2002 and 2008, 22% of all OEF/OIF veterans seen at the VA were diagnosed with PTSD at one or more encounter (Seal et al., 2009). Several potential reasons may contribute to this a discrepancy , including differences in the expression of PTSD among veterans and current service members and selection forces that result in a higher proportion of veterans with PTSD seeking VA care (Dursa et al., 2014). A number of recent studies have described heterogeneity within the longitudinal course of PTSD using latent growth mixture modeling (LGMM) (Berntsen et al., 2012; Bonanno et al., 2012; deRoon-Cassini et al.