The cross-trait correlations between the latent factor PGD scores and CU at 15 to 17 years, 18 to 21 years and 22 to 25 years were 0.65, 0.64 and 0.61 respectively. The monozygotic (MZ) and dizygotic (DZ) cross-twin cross-trait correlations at each epoch are shown in Table 1. Based on the 95% confidence intervals, all correlations were significantly different from zero, suggesting that familial aggregation accounts for some of the covariance between PGD and CU. All of the DZ twin pair cross-trait correlations were greater than half of the MZ twin pair cross-trait correlations which suggests that a combination of genetic and shared environmental likely explains the familial covariance.
