Consider the model you fit in Exercise 37 to predict Wal-Mart’s revenue from the Retail Index, CPI, and Personal Consumption index.
a) Plot the residuals against the predicted values and comment on what you see.
b) Identify and remove the four cases corresponding to December revenue and find the regression with December results removed.
c) Does it seem that Wal-Mart’s revenue is closely related to the general state of the economy?