a model including full A and E matrices and dropping the full C matrix representative of all shared environmental influences (Model III). The AIC decreased and the chi-squared change was nonsignificant for the change in degrees of freedom, indicating that the more parsimonious model dropping all shared environmental influences on the measures provided a better fit. Models IV to VI are submodels that test for a reduced number of genetic factors. We systematically tested the significance of each genetic factor and each pathway in the following sequence: (1) tested the significance of the entire A matrix; (2) tested the significance of each latent genetic factor; and (3) tested the significance of each individual genetic pathway. Each of the pathways retained in the best-fitting model is by definition significant. Model IV allows for only 1 latent genetic factor (A1 in Fig. 1), Model V allows for 2 latent genetic factors (A1 and A2), and Model VI allows for 3 latent genetic factors (A1, A2, and A3). For each of these submodels, the AIC increased and the chi-squared change was significant for the change in degrees of freedom, indicating that these models provided a worse fit to the data. The best-fitting model
