. Author manuscript; available in PMC: 2009 Jan 1.

Published in final edited form as: Learn Individ Differ. 2008;18(3):289–295. doi: 10.1016/j.lindif.2008.03.004

Table 4.

MX Model Fitting Estimates (and Confidence Intervals) for Latent Traits of Reading and Spelling Within Each Twin Sample at (a) Kindergarten and (b) Grade 1

Variables	a²	c²	e²
(a)
Reading
Australian sample	.84 (.61, .94)	.09 (.00, .31)	.08 (.05, .11)
U.S. sample	.68 (.54, .84)	.25 (.09, .39)	.07 (.05, .09)
Scandinavian sample	.33 (.11, .60)	.52 (.26, .71)	.15 (.10, .23)
Spelling
Australian twins	.74 (.44, .95)	.17 (.00, .45)	.10 (.04, .17)
U.S. twins	.44 (.27, .63)	.41 (.23, .56)	.15 (.10, .21)
Scandinavian twins	.46 (.17, .83)	.42 (.06, .68)	.12 (.06, .21)
(b)
Reading
Australian sample	.80 (.52, .87)	.02 (.00, .28)	.18 (.13, .26)
U.S. sample	.83 (.65, .92)	.07 (.00, .24)	.11 (.08, .14)
Scandinavian sample	.79 (.46, .89)	.07 (.00, .38)	.14 (.09, .22)
Spelling
Australian twins	.79 (.44, .95)	.00 (.00, .19)	.20 (.15, .28)
U.S. twins	.62 (.42, .78)	.13 (.00, .32)	.24 (.20, .31)
Scandinavian twins	.69 (.44, .82)	.09 (.00, .31)	.22 (.15, .33)

Note. Estimates with 95% confidence intervals including .00 are not significantly greater than 0.