Table 2.

Sibling fixed-effect estimates of birth weight (log ounces) on maternal time investments, using both continuous measures and linear piecewise splines for mother's education

	Total Time			Educational Time
	(1)	(2)	(3)	(4)	(5)	(6)
A. Full Sample
Log birth weight	0.08 (0.11)	0.15 (0.11)	0.18 (0.11)	–0.08 (0.15)	–0.02 (0.16)	0.13 (0.16)
Log birth weight × Education (years)		–0.01* (0.00)			–0.00 (0.01)
Log birth weight × 1st segment of spline (≤12)			–0.00 (0.00)			–0.01* (0.00)
Log birth weight × 2nd segment of spline (≤12)			–0.09† (0.05)			–0.14† (0.08)
N	1,516	1,516	1,516	1,516	1,516	1,516
Number of sibling pairs	758	758	758	758	758	758
B. Both Siblings <6 Years Old
Log birth weight	–0.07 (0.22)	2.83* (1.13)	2.30 (1.71)	–0.10 (0.21)	2.66* (1.22)	1.06 (1.66)
Log birth weight ×Education (years)		–0.23** (0.09)			–0.22* (0.10)
Log birth weight × 1st segment of spline (≤12)			–0.17 (0.15)			–0.06 (0.14)
Log birth weight × 2nd segment of spline (≤12)			–0.29* (0.13)			–0.36* (0.16)
N	594	594	594	594	594	594
Number of sibling pairs	297	297	297	297	297	297
C. Both Siblings ≥6 Years Old
Log birth weight	0.11 (0.13)	0.17 (0.13)	0.11 (0.13)	–0.22 (0.37)	–0.23 (0.35)	–0.07 (0.38)
Log birth weight × Education (years)		–0.01* (0.00)			0.00 (0.00)
Log birth weight × 1st segment of spline (≤12)			–0.01 (0.01)			–0.01 (0.01)
Log birth weight × 2nd segment of spline (≤12)			0.04 (0.12)			–0.18 (0.18)
N	380	380	380	380	380	380
Number of sibling pairs	190	190	190	190	190	190

Notes: Sibling fixed-effect models for the full sample include the following covariates: child's sex, an indicator for whether school aged, an indicator for whether the younger child, mother's age at birth, and an indicator for whether the mother was married at the child's birth. Age-stratified models include all the preceding covariates but exclude an indicator for whether school aged. Robust standard errors are shown in parentheses.

^†p < .10

^*p < .05

^**p < .01