Modified from Exercise 4.6

The following graphs are used to verify some of the assumptions of the ordinary least squares re- gression of Y on X1, X2, . . . , Xp: 1. The scatter plots of Y versus each predictor Xj . 2. The scatter plot matrix of the variables X1, X2, . . . , Xp. 3. The normal probability plot (QQ plot) of the internally studentized residuals. 4. The residuals versus fitted values. 5. Index plot of Cook's distance. For each of these graphs: (a) What assumption can be verified by the graph? (b) Sketch an example of the graph where the assumption does not seem to be violated. (c) Sketch an example of the graph which indicates the violation of the assumption.