Table 3.

Intraclass Correlations and Estimated Heritabilities Between Twins Within Latent Classes at Ages 7, 10, and 12

Twin Type	n pairs	Class
		Low or No Symptom	Defiant	Irritable	High Symptom
Age 7
MZM	605	0.65	0.643	0.333	0.476
DZM	679	0.457	0.349	0.014	0.137
MZF	675	0.617	0.63	0.252	0.405
DZF	622	0.435	0.415	0.016	0.134
DOS	1223	0.421	0.505	0.079	0.175
Heritability male		0.386	0.588	0.333	0.476
Heritability female		0.364	0.43	0.252	0.405
Age 10
MZM	498	0.69	0.524	0.279	0.574
DZM	510	0.43	0.365	−0.009	0.244
MZF	637	0.711	0.658	0.395	0.522
DZF	513	0.503	0.477	0.081	0.179
DOS	1122	0.393	0.325	0.018	0.132
Heritability male		0.52	0.318	0.279	0.574
Heritability female		0.416	0.362	0.395	0.522
Age 12
MZM	488	0.636	0.494	0.31	0.39
DZM	459	0.571	0.377	0.155	0.185
MZF	580	0.748	0.623	0.45	0.411
DZF	423	0.608	0.374	0.123	0.108
DOS	920	0.531	0.445	0.245	0.236
Heritability male		0.13	0.234	0.31	0.39
Heritability female		0.28	0.498	0.45	0.411

Note: Heritability is calculated using Falconer’s formula, except in situations where genetic dominance may be present (monozygotic [MZ] correlation >= 2 × dizygotic [DZ] correlation) in which case the MZ correlation is used as the estimate.

DOS = dizygotic twins of opposite sex; DZF = dizygotic female; DZM = dizygotic male; MZM = monozygotic male; MZF = monozygotic female.