The intraclass correlations are more similar than different for the two genders, and indicate substantial genetic influence on all composite measures (Table 3); MZ correlations were significantly greater than DZ correlations in all cases (all z-statistics > 2.80, p-values < .01). Although the DZ correlation for EXT was substantial for both genders, suggesting some influence of shared environment, it was not significantly greater than half the MZ correlation (p > .10).
