Table 2.

Estimates from Biometric Quadratic Growth Curve Models (Centered Post-l^st Grade) of Means, Variance, and Proportions of Variance in Intercept and Growth Due to Genetic and Environmental Influences.

		Intercept		Slope		Quadratic			Latent Intercept			Latent Slope			Latent Quadratic
Variable	Model	Mean	Var.	Mean	Var.	Mean	Var.	r Unique	a 2	c 2	e 2	a 2	c 2	e 2	a 2	c 2	e 2
TOWRE Sight KG – 4th	Indep.	38.24	184.20	21.12	29.66	−3.65	3.52	MZ = 0 DZ = 0	.85* [.68, .96]	.09 [.00, .27]	.05* [.03, .08]	.59* [.29, .87]	.33* [.06, .60]	.09* [.03, .16]	.72* [.41, .94]	.20* [.01, .49]	.08* [.03, .16]
	Correl.	38.23	182.91	21.10	26.62	−3.64	3.14	MZ = .53 DZ = .32	.83 * [.66, .93]	.09 [.00, .26]	.08 * [.06, .11]	.80 * [.46, .91]	.06 [.00, .37]	.14 * [.08, .23]	.86 * [.55, .93]	.01 [.00, .30]	.13 * [.07, .21]
TOWRE Decode KG – 4th	Indep.	16.21	81.04	9.39	16.60	−1.04	1.46	MZ = 0 DZ = 0	.90* [.73, .94]	.01 [.00, .18]	.08* [.06, .12]	.75* [.49, .92]	.15* [.002, .40]	.10* [.05, .17]	.79* [.50, .95]	.14* [.001, .41	.07* [.02, .16]
	Correl.	16.21	80.23	9.38	15.32	−1.03	1.27	MZ = .39 DZ = .14	.88 * [.69, .92]	.01 [.00, .19]	.11 * [.08, .15]	.79 * [.51, .92]	.08 [.00, .34]	.13 * [.08, .20]	.81 * [.55, .93]	.03 [.00, .29]	.15 * [.07, .26]

Note: Intercept is centered at the second time point (post-1^st grade). The four time points included: post-kindergarten, post-1^st, post-2^nd, and post-4^th. Indep. = Model without unique variances correlated; Correl. = Model with unique variance correlations, constrained within-zygosity; r_Unique = correlations for unique variances; MZ = monozygotic; DZ = dizygotic; a² = proportion of variance due to genetic influences; c² = proportion of variance due to shared environmental influences; e² = proportion of variance due to nonshared environmental influences. The endorsed final model, based on both better model fit and theoretical reasons, is shown in bold.

^*p < .05 determined using 95% confidence intervals, confidence intervals presented in brackets.