For the regression of PCI (Y) on YNG (X) for the African countries considered in Problem 2 in Chapter 12, use the accompanying information to do the following:
a. Plot the estimated straight-line and quadratic models on the scatter diagram for the data on the African countries.
b. Test for the significance of the straight-line regression and for the adequacy of fit of the straight-line model.
c. Test for the significance of the addition of the X2 term to the model.
d. Which model is more appropriate, the straight-line model or the quadratic model?
Degree 1 fit: Ŷ = 893.57 - 17.276
Degree 2 fit: Ŷ = 732.05 - 9.203X - 0.0996X2