13. Refer to the previous exercise, and use software to obtain regression diagnostics

a) Study the studentized residuals. Are there any clear outliers?

b) Study the liat values. Are there any observations with noticeable leverage?

c) Based on the answers in

(a) and (b). docs it seem as if any observations may be partic- ularly influential? Explain.

d) Study the DFFITS values. Which, if any. observations have a strong influence on the fitted values?

e) Study the DFBETAS values. For each term. which if any observations have a strong influence on the parameter estimate?

f) Remove the observation that seems most influential to you, and refit the model is the fit different in any substantive way?