Table 3.

Twin intraclass correlations and ACDE estimates from univariate model-fitting analyses

Measure	rMZ	rDZ	a2	d2	c2	e2
Age 9
Self-evaluation	.40 (.35–.45) n = 1040	.11 (.04–.17) n = 906	.02 (.00– .28)	.38 (.11– .45)		.59 (.55 – .64)
Math achievement	.68 (.64–.72) n = 741	.41 (.34–.47) n =658	.56 (.43 – .70)		.12 (.00 – .25)	.32 (.28– .35)
Age 12
Self-evaluation	.42 (.35–.48) n = 703	.18 (.10–.26) n = 593	.29 (.00 – .47)	.14 (.00 – .46)		.57 (.52 – .64)
Math achievement	.52 (.42–.61) n = 312	.39 (.25–.50) n = 263	.36 (.07– .61)		.17 (.00 – .42)	.46 (.38 – .56)

Note. rMZ= monozygotic twin correlation; rDZ = dizygotic (only same-sex twins are included) twin correlation; a² = the proportion of variance due to additive genetic effects; d² = the proportion of variance due to non-additive genetic effects; c² = the proportion of variance due to shared environments; e² = the proportion of variance due to non-shared environments; n = number of complete twin pairs. Self-evaluation was reported by children; Mathematics achievement was assessed by teachers according to the National Curriculum. 95% confidence intervals are included in parentheses.