Table 3.

Spline fit of natural-log lead specification and all independent variables with two degree of freedom splines.

Variable	dfa	Gain	Probability of gain
HOME	2	2.646	0.104
Birth weight	2	2.515	0.113
Maternal IQ	2	0.603	0.438
Maternal education	2	0.690	0.406
Natural-log lead	2	1.438	0.230

df, degrees of freedom. Total gain (nonlinearity χ²) = 7.894 (5.005 df), p = 0.1626.

^aApproximate.