We included covariates in our analyses to conduct a rigorous test of our hypotheses and reduce the likelihood that these variables could account for findings. All analyses were adjusted for age, sex, the first two ancestry principal components, deployment-related blast exposure (Fortier et al., 2014), handedness, current employment, and total cholesterol. Covariates were selected based on demonstrated associations with neural connectivity/integrity, genetic effects, and/or externalizing phenotypes in previous research (Han et al., 2014; Price et al., 2006; Spielberg et al., 2017). Given high rates of trauma exposure, PTSD, and mild TBI in this sample, we also examined whether these variables and other comorbidities altered study findings and found that they did not (see Supplemental Results for details). Correlations between the covariates and study variables are reported in the supplemental materials (Supplemental Table 1).
