Table 7. First-Order Condition (Eq. 4).

	TADI Total	TADI Cognitive	TADI Language	TADI Motor	TADI Socioemotional	Weight	Height	BMI
	Log ratio of Aggregate Parental Investments (twin i / twin j)
Log ratio of birth weight (twin i / twin j)	0.006 (0.011)	0.008 (0.013)	0.007 (0.013)	0.006 (0.010)	0.004 (0.009)	0.001 (0.008)	0.002 (0.008)	0.089 (0.185)
Constant	-0.001 (0.002)	-0.002 (0.002)	-0.001 (0.002)	-0.001 (0.002)	0.000 (0.001)	0.001 (0.001)	0.001 (0.001)	0.015 (0.030)
Observations	948	936	943	948	948	917	914	789

Note: Standard errors in parentheses. Estimates are significantly different from - ∞ and from 1.0, but not significantly different from 0.0.