The Schooling Quality-Earnings Relationship: Using Economic Theory to Interpret Functional Forms Consistent with the Evidence
James Heckman, Anne Layne-Farrar, Petra Todd
NBER Working Paper No. 5288
This paper investigates the economic and empirical foundations of the evidence relating earnings to schooling quality. We replicate the Card-Krueger model for Census years 1970, 1980 and 1990 and find that it consistently produces a strong relationship between schooling quality and the rate of return to schooling. We test key identifying assumptions used by Card and Krueger and others. Several assumptions are rejected. When they are relaxed, the evidence for a strong effect of schooling quality on earning is greatly weakened. A crucial identifying assumption is the absence of selective migration on the basis of earnings. Nonparametric tests strongly reject this hypothesis. The conventional assumption of linearity of the earnings- schooling relationship widely used in the literature is also rejected. The only surviving evidence of any schooling quality effect is in the return to college education. We also test and reject conventional efficiency unit models of the pricing of labor services. The empirically concordant model of earnings is a model of heterogeneous human capital in which regional shocks affect the prices of less- skilled labor.