For each of the following diagnostic tools, indicate what aspects of ordinary least squares are being checked and how the results might indicate problems. (a) Normal plot of r ∗ i . (b) Plot of e...

For each of the following diagnostic tools, indicate what aspects of ordinary least squares are being checked and how the results might indicate problems.

(a) Normal plot of r^∗
_i.

(b) Plot of e versus
. (c) Cook’s D.