TABLE 1.

Phenotypic Correlations, Twin Pair correlations, and Standardized Proportions of Variance Explained by Additive Genetic (A), Shared Environmental (C), and Non-Shared Environmental (E) Risk Factors

Variables	Pearson product moment correlations						Twin pair correlations		Univariate parameter estimates (95%)
	1	2	3	4	5	6	MZ	DZ	A	C	E
Difficult	1						0.56	0.12	0.48 (0.20 – 0.64)	0.00 (0.00 – 0.18)	0.52 (0.36 – 0.71)
Inhibited	0.19	1					0.52	0.48	0.07 (0.00 – 0.50)	0.46 (0.12 – 0.60)	0.48 (0.32 – 0.62)
Unsocial	0.19	0.12	1				0.53	0.26	0.46 (0.21 – 0.62)	0.00 (0.00 – 0.42)	0.54 (0.51 – 0.65)
Resistant	0.37	0.23	0.44	1			0.68	0.59	0.00 (0.00 – 0.43)	0.61 (0.51 – 0.70)	0.39 (0.28 – 0.60)
ADHD	0.14	0.08	0.03	0.08	1		0.71	0.19	0.61 (0.00 – 0.92)	0.00 (0.00 – 0.69)	0.38 (0.38 – 0.95)
ODD	0.13	0.16	0.02	0.05	0.25	1	0.55	0.45	0.21 (0.00 – 0.65)	0.34 (0.00 – 0.58)	0.45 (0.30 – 0.62)
SAD	0.10	0.13	0.01	0.07	0.42	0.31	0.43	0.29	0.28 (0.00 – 0.62)	0.15 (0.00 – 0.44)	0.57 (0.38 – 0.79)

Note: ADHD = attention deficit hyperactivity disorder, ODD = oppositional defiant disorder, SAD = separation anxiety disorder. Bold items represent significant correlations at α= 0.05.