Suppose that a response variable Y is related to four predictor variables, X1, X2, X3, and x4, so that k = 4. 1. Enter the observed values of y and each of the k = 4 predictor variables into the first (k + 1) columns of a MINITAB worksheet. Once this is done, the main inferential tools for multiple regression analysis are generated using Stat Regression Regression. The dialogue box for the Regression command is shown in Figure 13.21(a). 2. Select y for the Response variable and x1, x2,...,x for the Predictor variables. You may now choose to generate some residual plots to check the validity of your regression assumptions before you use the model for estimation or predic- tion. Choose Graphs to display the dialogue box for residual plots, and choose the appropriate diagnostic plot.