Determining sample size requirements for structural equation modeling (SEM) is a challenge often faced by investigators, peer reviewers, and grant writers. Recent years have seen a large increase in SEMs in the behavioral science literature, but consideration of sample size requirements for applied SEMs often relies on outdated rules-of-thumb. This study used Monte Carlo data simulation techniques to evaluate sample size requirements for common applied SEMs. Across a series of simulations, we systematically varied key model properties, including number of indicators and factors, magnitude of factor loadings and path coefficients, and amount of missing data. We investigated how changes in these parameters affected sample size requirements with respect to statistical power, bias in the parameter estimates, and overall solution propriety. Results revealed a range of sample size requirements (i.e., from 30 to 460 cases), meaningful patterns of association between parameters and sample size, and highlight the limitations of commonly cited rules-of-thumb. The broad “lessons learned” for determining SEM sample size requirements are discussed.

To describe the prevalence of posttraumatic stress disorder (PTSD) and comorbid psychiatric disorders and identify correlates of PTSD in a contemporary, nationally representative sample of US veterans. Data were analyzed from Wave 1 of the National Health and Resilience in Veterans Study, a cross-sectional, retrospective, web-based survey of a population-based sample of 3,157 US veterans conducted between October and December 2011. The main outcome measure was probable lifetime PTSD, which was assessed by using a DSM-IV version of the PTSD Checklist (PCL), the PCL-Specific Stressor version. The weighted lifetime and current prevalence of probable PTSD was 8.0% (standard error [SE] = 0.48) and 4.8% (SE = 0.40), respectively. 87.0% of veterans reported exposure to at least 1 potentially traumatic event (PTE); veterans reported a mean of 3.4 (SD = 2.8) different PTE types in their lifetime. Sudden death of a loved one was the most frequently endorsed PTE (61.3%), and sexual abuse in adulthood had the highest conditional probability of PTSD (37.3%). PTSD was associated with increased odds of mood, anxiety, and substance use disorders (odds ratios [ORs] = 2.2-19.1, P values < .001); suicidal ideation (OR = 9.7, P < .001); and suicide attempts (OR = 11.8, P < .001). Psychosocial factors, including resilience, community integration, and secure attachment, were associated with decreased odds of PTSD (ORs = 0.5-0.7, P values < .05). In a nationally representative sample of US veterans, the prevalence of lifetime and current PTSD was 8.0% and 4.8%, respectively, and PTSD was associated with elevated risk for several psychiatric conditions and suicidality. Veterans reported exposure to many PTE types in addition to combat, and conditional risk for PTSD was high for noncombat-related trauma. Prevention and treatment efforts designed to bolster protective psychosocial factors may help mitigate PTSD risk in this population.