genetic influences with PTSD. Studies have shown that genetic influences on PTSD may be around 30%–40% (Banerjee, Morrison, & Ressler, 2017; Nugent, Amstadter, & Koenen, 2008; Stein, Jang, Taylor, Vernon, & Livesley, 2002; True et al., 1993) and alcohol dependence around 50%–60% (Reilly, Noronha, Goldman, & Koob, 2017; Walters et al., 2018). Further, Sartor et al. showed that PTSD and alcohol dependence had a genetic correlation of 0.54 (Sartor et al., 2011). In addition, a recent study by Sheerin et al. on shared molecular genetic basis for alcohol dependence and PTSD showed lower heritability for PTSD and alcohol dependence (h 2 = 0.18 and 0.09, respectively) and a significant correlation between alcohol dependence and PTSD (r = .35) and a moderate, but significant correlation between alcohol dependence and PTSD (r = .34) in female participants (Sheerin et al., 2020). Although there are environmental and genetic contributions to both PTSD and alcohol dependence, most studies only examine dichotomous parental alcohol dependence status. A family history density (FHD) measure is useful for disorders influenced by genetic and environmental components, such as PTSD and alcohol dependence, since it can include other affected family members and account for degrees of relatedness (Cservenka, Gillespie, Michael,
