TABLE 1.

Means and Standard Deviations for Percentage of Correct Items and ANOVA Results by Sex and Zygosity for All Three Mathematics Measures

Measure	MZa		DZb		Malec		Femaled		MZ-me		DZ-mf		MZ-fg		DZ-fh		DZ-oppi		Sex		Zygosity		Sex × Zygosity
	M	SD	M	SD	M	SD	M	SD	M	SD	M	SD	M	SD	M	SD	M	SD	p	η2	p	η2	p	η2
Understanding Number	.76	.18	.77	.18	.78	.18	.75	.18	.78	.18	.79	.18	.75	.18	.75	.18	.77	.18	.000	.008	.377	.001	.458	.001
Non-Numerical Processes	.69	.18	.70	.17	.71	.17	.68	.17	.70	.18	.72	.16	.68	.17	.68	.17	.70	.17	.009	.003	.867	.000	.097	.002
Computation and Knowledge	.81	.19	.82	.19	.83	.19	.81	.19	.83	.18	.84	.19	.80	.20	.80	.20	.82	.19	.002	.003	.794	.000	.243	.001

Note. Descriptive statistics are reported on the whole sample after medical exclusions, N = 5,348. MZ = monozygotic twins; DZ = dizygotic twins (same and opposite sex); MZ-m = monozygotic male twins; DZ-m = dizygotic male twins; MZ-f = monozygotic female twins; DZ-f = dizygotic female twins; DZ-opp = dizygotic opposite-sex twins; η² = proportion of the total variance attributed to an effect.

^an = 1,941.

^bn = 3,407.

^cn = 2,413.

^dn = 2,935.

^en = 803.

^fn = 777.

^gn = 1,138.

^hn = 926.

ⁱn = 1,704.