To examine sex differences in heritability, we observed intra-pair correlations by zygosity and sex. Our sample only had 33 DZ female twin pairs, and because the opposite-sex DZ twin correlations (0.40) were generally similar to the DZ same-sex twin correlations (males = 0.47; females = 0.41) we did not further test sex differences in heritability. We could not examine differences in heritability by respondent because there were very few self-reporting twins (n = 54).
