Table 4.

Structural equation regression models predicting language outcomes at 18, 30, and 60 months from sleep ratios at 6 and 18 months

Model – Outcome	Step	Predictor	B (SE)	P	b	c2	df	P
18-month Language	1	Zygosity	0.19 (0.07)	0.008	0.11	19.54	15	0.19
		Sex	0.15 (0.04)	< 0.001	0.09
		Child covariables	−0.07 (0.05)	0.16	−0.04
		Mother covariables	0.11 (0.05)	0.03	0.09
		Language status	−0.22 (0.10)	0.02	−0.10
	2	6-month sleep ratio	−0.06 (0.02)	0.01	-0.07	23.85	19	0.20
30-month Language	1	Zygosity	0.00 (0.01)	0.83	0.01	16.36	15	0.36
		Sex	0.02 (0.01)	0.01	0.08
		Child covariables	0.00 (0.01)	0.89	0.00
		Mother covariables	0.03 (0.01)	0.004	0.12
		Language status	−0.07 (0.02)	< 0.001	−0.19
	2	6-month sleep ratio	−0.02 (0.01)	0.002	−0.11	19.85	19	0.40
	3	18-month sleep ratio	−0.00 (0.01)	0.84	−0.01	35.77	23	0.04
Adjusted for 18-month language	4	6-month sleep ratio	−0.01 (0.01)	0.01	−0.09	32.83	23	0.08
	5	18-month sleep ratio	−0.01 (0.01)	0.12	−0.06	50.68	27	0.004
60-month Language	1	Zygosity	0.06 (0.08)	0.81	0.03	12.70	15	0.63
		Sex	−0.06 (0.05)	0.30	−0.03
		Child covariables	−0.08 (0.06)	0.17	−0.04
		Mother covariables	0.49 (0.06)	< 0.001	0.34
		Language status	−0.85 (0.10)	< 0.001	−0.34
	2	6-month sleep ratio	−0.05 (0.03)	0.09	−0.06	21.39	19	0.32
	3	18-month sleep ratio	−0.07 (0.03)	0.05	−0.07	24.05	23	0.40
Adjusted for 30-month language	4	6-month sleep ratio	−0.04 (0.03)	0.22	−0.04	47.67	23	0.002
	5	18-month sleep ratio	−0.06 (0.03)	0.06	−0.07	49.80	27	0.005

The factor score for child covariables includes gestation duration, birth weight, Apgar score, number of days in the hospital after birth, and child difficult temperament. The factor score for maternal covariables includes education, family income, depressive symptoms, overprotectiveness, and impact perception.