Understanding the genetic and environmental contributions to overall phenotypic stability requires combining information concerning time-specific magnitude and cross-time stability of genetic and environmental factors. For example, a phenotype may be highly heritable at two time points (e.g., childhood and late adolescence), but if genetic stability is low across this period (e.g., as a result of gene activation and deactivation related to puberty), then genetic factors would not contribute to the stability of the phenotype. Similarly, a phenotype may be highly environmental at two time points, but the environmental influences (e.g., peer groups) may change during transitions to new environments (e.g., going from high school to college). The contributions of genetic and environmental effects to stability are calculated by multiplying the time-specific factor loadings by the associated latent variable correlation. For example, a1 × rA × a2 yields the genetic contribution to stability. Summing the contribution from A and E recaptures the standard test-retest correlation (i.e., phenotypic stability = [a1 × rA × a2] + [e1 × rE × e2]). Phenotypic stability results from genetic and environmental influences that persist through time.
