Trajectories of trauma symptoms and resilience in deployed US

The operations of the US military since 2001 have raised important concerns about the psychological costs of intense and repeated deployments. 1–3 Military personnel deployed for combat operations are frequently exposed to traumatic events and, predictably, those returning from the operations in Iraq and Afghanistan have evidenced increased rates of post-traumatic stress disorder (PTSD). 1,2 Unfortunately, it is difficult to accurately assess the psychological cost of deployment in these samples. 4 Although previous studies have made important advances in our understanding of deployment-related trauma reactions, with few exceptions 5,6 little prospective research among population-based samples exists to explain how trauma symptoms vary across time. These earlier studies have typically relied on convenience samples, which potentially introduce sampling bias and limit generalisability; use of assessment data that may be vulnerable to reporting bias; and cross-sectional research designs that cannot distinguish trauma reactions from pre-existing symptoms. The current investigation attempted to fill this knowledge gap by using data from a large population-based sample of military personnel, the Millennium Cohort Study, followed prospectively over nearly a decade. 7 A previous study using data from this cohort identified new-onset PTSD symptoms in 7.6–8.7% of deployers who reported combat experiences, compared with 1.4–2.1% of deployers who did not report combat experience. 2 What is not yet known, however, is how post-traumatic stress varies from pre-to post-deployment, the extent that different trajectories of post-traumatic stress might capture that variation and the predictors that might best inform those trajectories. To address these questions, we examined pre–post trajectories of post-traumatic stress from participants who had deployed at least once in support of these operations. To identify the trajectories, we employed latent growth mixture modelling (LGMM). Traditional statistical approaches used to examine mental health over time assume a single homogeneous distribution of change. 8 Recent advances suggest that responses to potential trauma are heterogeneous and explained by a finite set of longitudinal trajectories, 9 including chronically elevated post-traumatic stress following the event, continuous symptom elevations that preceded the event and elevated pre-deployment (baseline) symptoms followed by steady improvement. This previous research has also repeatedly demonstrated resilient outcomes characterised by a stable trajectory of healthy adjustment (for example little or no symptoms pre-to post-event). 10 Latent growth mixture modelling is well-suited to capture these trajectories because it explicitly assumes outcome heterogeneity. 11 Of note, LGMM has been used effectively to identify prototypical trajectories following different types of potential trauma, including …