13.13. Refer to the previous exercise. Conduct the analyses for the interaction model and for comparing that model to the no-interaction model, as shown in Sections 13.3 and 13.4, after adding these data.

13.14. 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 + 0.8.v - 0.6z. The mean education is 11 for nonwhites and 13 for whites. The overall mean of father's education is 12 years.

(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.

Concepts and Applications