Table 2.

Sources of genetic and environmental variance for each phenotype.

Shared Liability Model
Genetic Influences	MD	INIT	FTND
Total genetic variance*	0.28	0.70	0.60
% from A1	100	4.8	22.1
% from A2	n/a	95.2	5.3
% from A3	n/a	n/a	72.6
Environmental Influences
Total environmental variance	0.72	0.30	0.40
% from E1	100	n/a	n/a
% from E2	n/a	100	3.6
% from E3	n/a	n/a	96.4
Causal Model
Genetic Influences	MD	INIT	FTND
Total genetic variance	0.27	0.69	0.61
% from A1	90.1	n/a	n/a
% from A2	1.5	100	15.5
% from A3	8.4	n/a	84.5
Environmental Influences
Total environmental variance	0.73	0.31	0.39
% from E1	97.6	n/a	n/a
% from E2	<1	100	10.5
% from E3	2.2	n/a	89.5

^*Note that, because twin modeling was conducted using ordinalized variables, the total phenotypic variance for each trait is constrained to 1; thus, these values are actually proportions of variance rather than true variance. However, totals might not sum to 1 due to rounding.