Differences by zygosity were significant in EA families only, where dizygotic (DZ) twins were at increased likelihood of sexual onset compared to monozygotic (MZ) twins (log-rank X21=4.37, p<0.05). Differences in parental alcoholism by zygosity were also significant in EA families, where more parents of DZ twins were coded positive for alcoholism compared to MZ twins (37% versus 34%, X21=4.47, p<0.05). Although zygosity was unrelated to parental separation in either AA or EA families, given differences in EA families, zygosity was included as an additional covariate in adjusted Cox regression models.
