Table 4.

Estimates of additive genetic (a²), shared environmental (c²), and non-shared environmental (e²) influences for the eight behavioral factors

Behavioral Composites	Variance component estimate (95% confidence interval)			Age moderation model fit statistics
	a2	c2	e2	${\chi }_{\mathrm{diff}}^2$	df	p	AIC
Academic Achievement	0.43* (0.01, 0.75)	0.01 (0.00, 0.15)	0.55* (0.25, 0.90)	0.00	1	0.99	–2.00
Total IQ	0.65* (0.29, 0.92)	0.19* (0.08, 0.30)	0.16 (0.00, 0.48)	2.27	1	0.10	0.72
Substance use disorders	0.10 (0.00, 0.49)	0.21* (0.08, 0.32)	0.66* (0.35, 0.87)	7.49	1	<0.01	5.49
Externalizing disorders	0.13 (0.00, 0.51)	0.22* (0.10, 0.33)	0.64* (0.33, 0.85)	0.21	1	0.65	–1.79
Internalizing disorders	0.39 (0.00, 0.76)	0.20* (0.08, 0.31)	0.41* (0.11, 0.78)	2.07	1	0.15	0.07
Peer groups	0.29 (0.00, 0.67)	0.14* (0.02, 0.27)	0.56 (0.26, 0.86)	1.42	1	0.23	–0.58
Disinhibitory behavior	0.23 (0.00, 0.61)	0.20* (0.07, 0.32)	0.57* (0.27, 0.84)	0.00	1	1.00	–2.00
Negative emotionality	0.18 (0.00, 0.58)	0.11 (0.00, 0.23)	0.71* (0.38, 0.95)	0.00	1	0.99	–2.00

95% confidence intervals were computed via Mx. The final four columns summarize the fit statistics for the ACE model in which the c² estimate is allowed to vary as a function of the difference in age between the siblings in each pair. Significant results indicate a better fit when the age-moderated component of c² is allowed to vary freely

^*Significant parameter estimates (the 95% CI's do no include zero)