For the data on VOTE (Y) and TVEXP (X) in Problem 5 in Chapter 5, it was found that the straight-line model was adequate. Using the accompanying computer output for quadratic regression, do the following:
a. Plot the fitted straight-line model and the fitted quadratic model on the scatter diagram for the data of this problem.
b. Determine the change in R2 in going from a degree 1 to a degree 2 model.
c. Test for the significance of the addition of the X2 term to the model.
d. Assess whether the results in parts (a) through (c) contradict your earlier conclusion about the adequacy of fit of the straight-line model.