For Exercises 2.77 to 2.79, see page 101; and for 2.80, see page 102.
2.89 Education and income
There is a strong positive correlation between years of schooling completed and lifetime earnings for American men. One possible reason for this association is causation: more education leads to higher-paying jobs. But lurking variables may explain some of the correlation. Suggest some lurking variables that would explain why men with more education earn more.