[h2: 2(rMZ–rDZ)=2(0.27–0.11)], dominant genetic effect accounts for approximately 10% [d2: 2(rMZ–rDZ)=2(0.27)–4(0.11)], and the nonshared environment accounts for the remaining 58% of the variance. The heritability of aggressive behavior based on self-reports is 40% and the nonshared environment accounts for the remaining 60% of the variance. There is no evidence of shared environmental contribution, as the DZ correlation is approximately half the MZ correlation. The heritability of aggressive behavior based on teacher ratings is 54%, shared environmental influences account for 6% [c2: 2rDZ–rMZ=2(0.33–0.60)], and the nonshared environment accounts for the remaining 40% of the variance. The heritability of aggressive behavior based on parent/caregiver ratings is 54%, shared environmental influences account for 17%, and the nonshared environment accounts for the remaining 29% of the variance. Thus, parent/caregiver ratings have the largest familial influence, explaining 71% of the variance (h2 + c2 = 0.54% + 17%) in individual differences in aggressive behavior. It should be kept in mind that this is a descriptive approach and that formal modeling is required to determine how well these estimates describe the observed data. Also, this approach does not allow for actual testing of different hypotheses, for example, to test whether it is possible to set any
