Patterns of treatment response in chronic posttraumatic stress disorder: an application of latent growth mixture modeling.

This study attempts to differentiate groups of individuals who exhibit different patterns of recovery following treatment for chronic posttraumatic stress disorder (PTSD) and describes these groups in terms of relevant characteristics at program intake. A sample of 2,219 Vietnam veterans who had completed a 12-week treatment program was followed up at 6, 12, and 24 months post admission using self-report measures. With change in PTSD symptoms over time as the focus, latent growth mixture modeling was used to assign individual veterans to subgroups. A three-group solution provided the best account of the data. Two groups showed moderate and consistent improvement over time although the larger group (n = 1,380) began treatment with more PTSD symptoms and improved more quickly over time. The smallest group (n = 87) showed a substantially different trajectory, with almost no net change in symptom levels over the 24-month period. The groups also varied significantly in terms of their characteristics, with symptom severity and improvements over time reflecting greater comorbidity and younger age. The results have both research and clinical implications.