Access the data, labeled Professor_Salary, from the text website. These data were used in the introductory case of this chapter. Recall that we estimated our preferred model as y̅ = 39.43 + 1.24x + 13.89d, where y represents salary (in $1,000s), x represents experience (in years), and d is a gender dummy variable that equals 1 for male and 0 for female.

a. Use the preferred model to construct the 90% prediction interval for the salary of a male professor with 20 years of experience.

b. Use the preferred model to construct the 95% prediction interval for the salary of a male professor with 20 years of experience.

c. Comment on the width of the above prediction intervals.