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Figure 4 College Wage Premium, OLS Regressions, Adjusted Wages
for 1967–2008 by their year- and sex-specific adjustment factors before taking logs of all wage values.
10
When I reestimate college wage premiums using adjusted wages, a very different picture emerges. See Figures 4 and 5.
11
I find little or no gender difference in the college wage premium since about 1990.
B. Tobit Regression Estimates
An alternate, and indeed simpler, way to correct for topcoding is to employ the Tobit censored regression model. This model treats
in Equation 1, annual wage income, y
i
as a latent variable, whose observed values are censored at an upper limit equal to the topcode value for the relevant year. This specification yields results almost iden-
tical to estimates based on adjusted wages. See Figures 6 and 7. There is essentially no significant gender difference in the college wage premium since about 1990.
C. Quantile Regression Estimates
I next run quantile median regressions, using the same set of regressors. Figures 8 and 9 present the results of the quantile regressions. Importantly, these results are
insensitive to the presence of topcodes or corrections for topcoding. In these esti-
10. Hirsh and McPherson 2008 provide estimates of by year starting in 1973 and sex based on
R supplemental CPS data on hourly wages. Larrimore et al. 2008 utilize internal-use CPS files to provide
mean wages of all topcoded observations in the same sex-by-race-by-FTFY-status demographic cell com- parable to those available in public-use files for 1995–2008 for all years starting in 1975. Using either of
these sources to adjust topcoded values yields results virtually identical to those presented here. 11. Note that the standard errors do not account for estimation of adjustment factors.
580 The Journal of Human Resources
Figure 5 Gender Difference in the Premium, Adjusted OLS Regressions, with 95 Percent
Confidence Interval Bands
Figure 6 College Wage Premium, Tobit Regressions with Censoring at Topcode
mates, the female-male difference is larger in earlier years, but the difference narrows and then vanishes by 2000.
12
12. A comparison of coefficients and standard errors for recensored and adjusted OLS, Tobit, and median regressions appears in Table 2.
Hubbard 581
Figure 7 Gender Difference in the Premium, Tobit Regressions, with 95 Percent Confidence
Interval Bands
Figure 8 College Wage Premium, Quantile Regressions
D. The Advanced Degree Wage Premium
