Table 2.

Covariance (cov) matrices, correlation (cor) matrices; and proportions, based on the ADE twin model.

	Phenotypic cov matrix			Phenotypic cor matrix
ΣPh	SP	SC	GRIT	SP	SC	GRIT
SP	11.725	6.207	6.615	1.000	0.474	0.502	-
SC	6.207	14.616	10.565	0.474	1.000	0.718	-	-
GRIT	6.615	10.565	14.824	0.502	0.718	1.000	-	-	-

	A cov matrix			A cor matrix			proportions ΣA/ΣPh
ΣA	SP	SC	GRIT	SP	SC	GRIT	SP	SC	GRIT
SP	9.009	4.806	4.868	1.000	0.653	0.996	0.768	0.774	0.736
SC	4.806	6.006	2.852	0.653	1.000	0.715	0.774	0.411	0.270
GRIT	4.868	2.852	2.649	0.996	0.715	1.000	0.736	0.270	0.179

	D cov matrix			D cor matrix			proportions ΣD/ΣPh
ΣD	SP	SC	GRIT	SP	SC	GRIT	SP	SC	GRIT
SP	0.288	0.587	1.220	1.000	0.543	0.792	0.025	0.095	0.184
SC	0.587	4.054	5.449	0.543	1.000	0.943	0.095	0.277	0.516
GRIT	1.220	5.449	8.239	0.792	0.943	1.000	0.184	0.516	0.556

	E cov matrix			E cor matrix			proportions ΣE/ΣPh
ΣE	SP	SC	GRIT	SP	SC	GRIT	SP	SC	GRIT
SP	2.428	0.813	0.527	1.000	0.244	0.170	0.207	0.131	0.080
SC	0.813	4.557	2.264	0.244	1.000	0.535	0.131	0.312	0.214
GRIT	0.527	2.264	3.936	0.170	0.535	1.000	0.080	0.214	0.265

The results are conditional on the sex and SES effects, and the random rater (teacher) effects. The values shown in bold are the standardized variance components. For instance for school performance, 76.8% is attributable to additive genetic factors (i.e., the narrow-sense heritability is 0.768), 2.5% is attributable to genetic dominance factors (i.e., the broad-sense heritability is 0.793), and 20.7% is attributable to non-shared environmental influences and measurement error.