Intraclass correlations by zygosity, genetic model parameter estimates, and nested model statistics of each variable controlling for age and nonverbal reasoning.

Note. Number of twin pairs ranged from 210 to 227 for MZ and from 80 to 84 for DZ. All ACE models had a satisfactory goodness of fit indicated by a nonsignificant χ2change between the saturated and the ACE models (Δχ2 ranged from 0.81 to 6.77, Δdf = 6, ps>.05). MZ = Monozygotic twins; DZ = Dizygotic twins; a2 = additive genetic variance; c2 = shared environment variance; e2 = nonshared environment variance; Δχ2 and Δdf are the differences between the ACE and the nested models.
(95% confidence intervals in parentheses).