Table 3.

Genetic and unique environmental variances and covariances

	Genetic influences			Environmental influences
Phenotype	Total variance	Total covariance with AD	Covariance shared only with AD	Total variance	Total covariance with AD	Covariance shared only with AD
CDa	.28	.28	.08	.51	<.01	<.01
FORGET	.29	.22	.05	.71	-.08	-.09
INATT	.34	.19	.00	.66	<.01	.03
HYPER	.31	.25	.13	.69	<-.01	<-.01
ADb	.50	N.A.	N.A.	.50	N.A.	N.A.

Notes: The total variance, total covariance with AD, and covariance specific to each phenotype with alcohol dependence (AD) are presented; both are derived from models in which the phenotype is adjacent to AD in the twin model, which is required for the calculation of the residual variance. Estimates are based on full models, before testing the significance of genetic and environmental covariance specific to AD and the other phenotypes.

^aShared environmental influences account for the remaining variance (21 %);

^bderived from a model structured as in Figure 1. CD = conduct disorder; FORGET = forgetfulness; INATT = inattention; HYPER = hyperactivity/impulsivity; N.A. = not applicable.