twins. E is by definition unique to each individual. Models were fit to data from four-member families as well as based only on twins, the latter to facilitate comparisons between the present results and published data, which is predominantly based on twin data. Additional detail concerning our model-fitting approach is provided in Iacono et al. (Iacono et al., 2014). As noted in that paper, we also evaluated possible dominance (D) effects, and fit and report the results of ADE model fitting in the twin sample where appropriate. Because variances tended to differ between males and females as well as between adolescents and adults (see Table 2 in Iacono et al., 2014, this issue), dummy variables representing these two characteristics were included as (scalar) moderators of phenotype variance in our biometric models.
