For each of the following questions, choose the one you would use (for example, a plot or an influence statistic) to answer the question. Describe your choice and what you would expect to see if there...

For each of the following questions, choose the one you would use (for example, a plot or an influence statistic) to answer the question. Describe your choice and what you would expect to see if there were no problem.

(a) Do the ϵ_i
have homogeneous variance?

(b) Is the regression being unduly influenced by the 11th observation?

(c) Is the regression on X₃
really linear as the model states?

(d) Is there an observation that does not seem to fit the model?

(e) Has an important independent variable been omitted from the model?