The correlation between the mother and father latent externalizing factor was medium to large (r = 0.45, 95% CI = 0.35-0.55), indicative of assortative mating. For the general transmission effects, the parent-child correlations for the latent externalizing factors were medium for biological mothers (r = 0.27, 95% CI = 0.20-0.34) and fathers (r = 0.30, 95% CI = 0.23-0.38), but were not significantly different from zero for adoptive mothers (r = 0.07, 95% CI = -0.01-0.15) and fathers (r = 0.03, 95% CI = -0.07-0.12). Families that included both a biological and adoptive offspring provided a particularly elegant demonstration of this pattern of family transmission. The general transmission effects were significant for biological children (mother r = 0.26, 95% CI = 0.14-0.37; father r = 0.35, 95% CI = 0.25-0.46), but not for adoptive children (mother r = 0.06, 95% CI = -0.02-0.14; father r = 0.02, 95% CI = -0.07-0.11). These findings suggest that parent-child resemblance on externalizing disorders is almost entirely attributable to genetic transmission. We also tested whether the general transmission effects differed by mother and father.
