Table 3.

Intraclass correlations and latent class heritability for monozygotic and dizygotic twins.

	Class Twin 2
	Alcohol Co-Use	Sim. Alcohol Use	Sim. Tobacco Use	Sim. ATD Use
Class Twin 1	Monozygotic Female Twins (208 pairs)
1	0.54	0.33	−0.39	−0.20
2	0.21	0.23	−0.14	−0.17
3	−0.26	−0.21	0.32	0.01
4	−0.26	−0.17	0.09	0.26
	Dizygotic Female Twins (148 pairs)
1	0.20	0.09	−0.09	−0.12
2	0.21	0.21	−0.18	−0.10
3	−0.06	−0.08	0.12	−0.02
4	−0.26	−0.15	0.11	0.21
	Monozygotic Male Twins (98 pairs)
1	0.42	0.06	0.00	−0.09
2	0.09	0.26	−0.06	−0.28
3	−0.05	−0.27	0.22	0.13
4	−0.07	−0.05	−0.13	0.21
	Dizygotic Male Twins (75 pairs)
1	0.09	0.08	−0.04	−0.05
2	0.03	0.15	−0.10	−0.08
3	−0.05	−0.13	0.15	0.03
4	−0.01	−0.08	0.01	0.08
	Dizygotic Opposite Sex Twins (130 pairs)
Class Female Twin	Class Male Twin
1	0.04	0.19	−0.08	−0.15
2	0.02	0.08	−0.02	−0.07
3	−0.02	−0.06	0.01	0.06
4	−0.01	−0.15	0.06	0.10
Estimated Heritability of Latent Class Membership
	Alcohol Co-Use	Sim. Alcohol Use	Sim. Tobacco Use	Sim. ATD Use
Females	68%	4%	40%	10%
Males	66%	22%	14%	26%
Full Sample	58%	12%	30%	14%