Several studies have analyzed longitudinal data on posttraumatic stress symptoms (PTSS) from individuals who were proximal to the September 11, 2001, terrorist attacks (9/11) in an attempt to identify different trajectories of mental health in the years following mass trauma. The results of these studies have been heterogeneous, with researchers who used latent growth mixture modeling (LGMM) tending to identify four trajectories and those who used group-based trajectory modeling (GBTM) identifying five to seven trajectories. Given that no study has applied both GBTM and LGMM to their data, it remains unknown which modeling approach and what number of trajectories best fit post-9/11 PTSS data. The present study aimed to address that question by applying both LGMM and GBTM to data from the largest sample of survivors to date, comprising 37,545 New York City community members. When analyzing four waves of PTSS, reflecting participants' mental health up to 15 years post-9/11, LGMM fit the data better than GBTM. Our optimal solution consisted of four trajectories: low-stable (72.2% of the sample), decreasing (12.8%), increasing (9.5%), and high-stable (5.5%) symptoms. Covariate analyses indicated that economic factors (i.e., having a household income less than $25,000 and experiencing job loss due to 9/11) increased the odds of belonging to the high-stable symptom trajectory group to the greatest degree, ORs = 4.93-6.08. The results suggest that providing financial support, including affordable mental health care, could be an important intervention in the wake of future mass traumatic events.
