There was evidence of a significant sex by zygosity interaction in predicting the frequency of adult contact (b = 0.24; t(2,024) = 2.54, p = .01). The greater frequency of adult contact among MZ compared to DZ twins was more apparent for males than females. Further, the frequency of adult contact was related to twin concordance (scored dichotomously) for AAB for females (OR = 1.22, 95% CI: 1.05, 1.41) but not males (OR = 1.14, 95% CI: 0.96, 1.36), though this difference was not significant (b = -.07, p = .56). Overall, these results could suggest a violation of the EEA among females. However, a relationship between frequency of adult contact and adult antisocial behavior among females is causally ambiguous – it is as consistent with the interpretation that more adult contact causes female twins to be more alike in their antisocial behavior as the interpretation that similarity in antisocial behavior leads to more frequent contact (Lykken, McGue, Bouchard, & Tellegen, 1990).
