Information describing 98 of the top automobile dealership groups in the United States is provided in computer database file DEALERS. For each group, the data include (1) total group revenue during 1999, (2) the number of retail vehicles sold that year, and (3) the number of dealerships in the group.
a. Determine the least-squares regression equation for y = total group revenue as a function of x1 = number of retail vehicles sold and x2 = number of dealers in the group. Interpret each of the partial regression coefficients.
b. At the 0.02 level, is the overall regression equation significant?
c. Use the 0.02 level in concluding whether each partial regression coefficient differs significantly from zero.
d. Construct a 98% confidence interval for each partial regression coefficient in the population regression equation.