Table 7.

Comparison of heritability estimates (Est) for the full sample, specific language impairment (SLI), and nonspecific language impairment (NLI) groups at −1.00 SD affectedness.

Outcome	Age	Full sample		SLI		NLI
		Est	SE	Est	SE	Est	SE
PPVT-III Vocabulary	4	.64	.24	.35	.32
	6	.86	.37	.64	.44
TOLD-P:3 Spoken Language	4	.36	.19	.34	.26	−.50	.62
	6	.65	.19	.45	.22	.74	.57
TOLD-P:3 Semantics	4	.28	.24	.44	.28	−.42	.63
	6	.52	.25	.60	.27	.86	.53
TOLD-P:3 Syntax	4	.69	.19	.45	.24	.27	.47
	6	.63	.19	.55	.22	.85	.56
GFTA-2 Speech	4	.24	.28	.00	.36
	6	.52	.50	1.22	.32
MLU	4	.83	.27	.91	.34	−.75	.65
	6	.74	.29	.74	.32
TEGI Composite	4	.48	.16	.33	.21	−.06	.50
	6	.71	.20	.71	.21
TEGI Screener	4	.54	.16	.26	.22	.18	.45
	6	.29	.24	.26	.27

Note. Negative heritability estimates occurred when the intraclass correlation for dizygotic twins was greater than the intraclass correlation for monozygotic twins, and heritability estimates greater than 1 occurred in models where the intraclass correlation for monozygotic twins was .5 greater than the intraclass correlation for dizygotic twins. Heritability estimates are not reported for combinations in which one of the four cells in the Twin × Affectedness combination was empty within zygosity (for which the associated tetrachoric correlation is not reliable due to small Ns within a group). PPVT-III = Peabody Picture Vocabulary Test–III; TOLD-P:3 = Test of Language Development–Primary: Third Edition; GFTA-2 = Goldman-Fristoe Test of Articulation–Second Edition; MLU = mean length of utterance as calculated by SALT software; TEGI = Rice–Wexler Test of Early Grammatical Impairment; CMMS = Columbia Mental Maturity Scale.