. Author manuscript; available in PMC: 2014 Jun 24.

Published in final edited form as: Behav Genet. 2009 Apr 18;39(4):437–445. doi: 10.1007/s10519-009-9271-2

Table 1.

MZ and DZ probandwise concordances and results of univariate DF extremes analysis using an 85% cut-off

	Probandwise concordance		Twin group correlation		DF estimates
	MZ	DZ	MZ	DZ	h²g (SE)	c²g (SE)	e2g (SE)
General Cognitive Ability	0.53	0.37	0.71	0.50	0.42 (.07)	0.30 (.05)	0.28 (.05)
Reading	0.62	0.39	0.79	0.50	0.59 (.07)	0.20 (.05)	0.21 (.04)
Math	0.52	0.43	0.73	0.57	0.32 (.07)	0.40 (.05)	0.28 (.04)
Language	0.47	0.35	0.64	0.47	0.34 (.07)	0.30 (.05)	0.36 (.05)

Note.

MZ = monozygotic; DZ = dizygotic; h²g = group heritability; c²g = group shared environment; e²g = group non-shared environment. Preliminary analyses revealed no significant sex differences, so to increase power we combined same-sex and opposite-sex dizygotic twins.

For each scale the number of complete twin pairs was as follows:

General cognitive ability: MZ = 1464; DZ = 2418. Reading: MZ = 1852; DZ = 3180. Math: MZ = 1696; DZ = 2896. Language: MZ = 1537; DZ = 2575.