6. Your friend has an on-campus job making telephone calls to alumni asking for donations to your college's annual fund, and she wonders 12. Fabio Silva and Jon Sonstelie, "Did Serrano Cause a Decline in School Spending?" National Tax Review, Vol, 48, No. 2. pp. 199-215. The authos also included the tax price for spending per pupil in the ith state as a variable. EXERCISES 27 whether her calling is making any difference. In an attempt to mea- sure the impact of student calls on fund raising, she collects data from 50 alums and estimates the following equation: GIFT, = 2.29 + 0.001INCOME, + 4.62CALLS, (1.26) where: GIFT, the 2016 annual fund donation (in dollars) from the ith alum INCOME the 2016 estimated income (in dollars) of the ith alum CALLS, the # of calls to the ith alum asking for a %3D donation in 2016 a. Carefully explain the meaning of each estimated coefficient. Are the estimated signs what you expected? b. Why is the left-hand variable in your friend's equation GIFT, and not GIFT? c. Your friend didn't include the stochastic error term in the estimated equation. Was this a mistake? Why or why not? d. Suppose that your friend decides to change the units of INCOME from "dollars" to "thousands of dollars." What will happen to the estimated coefficients of the equation? Be specific. e. If you could add one more variable to this equation, what would it be? Explain.