We examined sex differences in the veracity of the EEA in both childhood and adulthood. There was no evidence of a sex by zygosity interaction in predicting similarity of twin childhood environments (t(2,080) = -0.76, p = .45), indicating that the difference between MZ and DZ twins in similarity of childhood environments was not different for males and females. Further, after controlling for zygosity, twin similarity of childhood environment was not related to twin concordance for CD (scored dichotomously) for females (OR = 1.20, 95% CI: 1.00, 1.44). For males, greater similarity of childhood environment decreased the odds of twin concordance for CD, after controlling for zygosity (OR = 0.78, 95% CI: 0.64, 0.96). Thus, for males there was evidence that the more dissimilar the childhood environment, the greater the likelihood of twin concordance for CD. Overall, these results suggested that the EEA was not violated for either sex for CD.
