as error variance) were not overlapping across the two assessments. Thus, the best-fitting model (Model 9) included additive genetic influences that were common to ages 12 and 14 and age-specific non-shared (individual) environmental influences. Standardized parameter estimates for this model are shown in Fig. 1, and heritability estimates under this model can be found in Table 1. At both ages, heritability was significant, with a slight increase at age 14. Importantly, because age-specific genetic influences at age 14 could be dropped completely, genetic correlation between DD at different ages was 1.0.
