Table 2.

Intraclass Twin Correlations and Univariate ACE Estimates (95% Confidence Intervals)

	MZ twin pairs (n = 902)	DZ twin pairs (n = 480)	A	C	E
Parent-Child Relationship Problems at age 18	.57 (.52, .62)	.36 (.27, .45)	.43 (.25, .61)	.15 (.00, .31)	.42 (.38, .47)
Externalizing at age 18	.70 (.66, .73)	.42 (.34, .50)	.66 (.52, .75)	.07 (.00, .20)	.27 (.24, .31)
Parent-Child Relationship Problems at age 25	.46 (.40, .52)	.26 (.16, .35)	.38 (.17, .51)	.08 (.00, .27)	.54 (.49, .60)
Externalizing at age 25	.60 (.55, .64)	.31 (.23, .40)	.62 (.46, .66)	.00 (.00, .14)	.38 (.34, .42)

NOTE: MZ = Monozygotic, DZ = dizygotic. A = Additive genetic variance, C = Shared environmental variance, E = Nonshared environmental variance. Ninety-five confidence intervals are shown in parentheses; the estimate is significantly different from zero if the interval does not cross zero.