To assess the reliability of the results obtained from the complex model used here, we also stratified the sample into 3 equal categories according to levels of PPD (Low, Moderate, and High), and estimated the total variance, as well as ADV, CDV, and EDV for DV in each PPD category independent of the genetic moderation model. For this analysis, twin pairs were included if they scored in different categories, e.g. one scored low and the co-twin scored high, by using a model that accounts for this by utilizing the ‘definitional variable’ options in Mx. Consistent with the findings reported for the full model described above, we found that the total variance was high in the low PPD group (0.74), decreased in the moderate PPD group (0.50), and increased in the high PPD group (1.49). Furthermore, estimates of ADV, CDV, and EDV showed similar patterns to those reported for the full model described above. The ADV was highest among adolescents with low PPD, low among those with moderate PPD and increased among adolescents with high PPD (low PPD: 0.63; moderate PPD:
