Table 2.

Twin similarity coefficients (intraclass correlations) for mathematics, reading and g

Measure	MZ	DZS	DZO	DZall	MZM	MZF	DZM	DZF
Mathematics	0.71 (0.68–0.75), (n = 863)	0.51 (0.45–0.56), (n = 762)	0.43 (0.37–0.49), (n = 751)	0.47 (0.43–0.51), (n = 1513)	0.69 (0.63–0.74), (n = 356)	0.73 (0.68–0.77), (n = 507)	0.47 (0.38–0.55), (n = 343)	0.54 (0.47–0.60), (n = 419)
Reading	0.64 (0.60–0.67), (n = 919)	0.44 (0.39–0.50), (n = 817)	0.42 (0.36–0.47), (n = 805)	0.43 (0.39–0.47), (n = 1622)	0.64 (0.58–0.70), (n = 383)	0.63 (0.58–0.68), (n = 536)	0.43 (0.34–0.51), (n = 373)	0.46 (0.38–0.53), (n = 444)
g	0.71 (0.67–0.74), (n = 833)	0.53 (0.47–0.58), (n = 728)	0.44 (0.38–0.50), (n = 709)	0.48 (0.44–0.52), (n = 1437)	0.71 (0.65–0.76), (n = 342)	0.71 (0.66–0.75), (n = 491)	0.50 (0.42–0.58), (n = 328)	0.54 (0.47–0.61), (n = 400)

All similarity coefficients are based on age-, sex- and download-time-corrected scores.

95% confidence intervals in parentheses.

Dzall, all DZ pairs; DZO, opposite-sex DZ pairs; DZS, same-sex DZ pairs; MZ, MZ pairs; MZF, MZ female pairs; MZM, MZ male pairs; n, number of twin pairs.