13.13. Exercise 13.1 reported the regression equation relating y = education to race (z = 1 for whites) and to father’s education (x) of E(y) = 3 + 0.8x − 0.6z. The means ¯y = 11 for nonwhites, ¯y = 13 for whites, and overall

¯y = 12.

(a) Find the adjusted mean educational levels for whites and nonwhites, controlling for father’s education.

(b) Explain why the adjusted means differ as they do from the unadjusted means.