. Author manuscript; available in PMC: 2014 Dec 1.

Published in final edited form as: J Speech Lang Hear Res. 2014 Jun 1;57(3):850–864. doi: 10.1044/2013_JSLHR-L-12-0240

Table 5. Proband-wise concordance, tetrachoric correlations, and liability threshold model results for LI at 4 years: Direct comparison for the psychometric LI and parent-referral groups.

Classification	N		Proband-wise concordance		Tetrachoric correlations		Liability threshold parameter estimates 95% CI
Classification	MZ	DZ	MZ	DZ	MZ	DZ	a ²	c ²	e ²
Psychometric LI	226	115	.90	.73	.96	.84	.18 [.06-.36]	.77 [.60-.89]	.04 [.02-.07]
Parent referral	112	104	.65	.35	.77	.40	.73 [.30-.85]	.04 [.00-.41]	.23 [.14-.35]
Both psychometric LI and parent referral	71	51	.95	.48	.99	.67	.64 [.34-1.00]	.35 [.00-.66]	.01 [.00-.03]

Note. CI = confidence interval; a² = heritability; c² = shared environmentality; e² = nonshared environmentality.