The multiple regression relationships of SBP (Y) to AGE (X1), SMK (X2), and QUET (X3) are studied. Three regression models are considered, yielding least-squares estimates and ANOVA tables as shown in the accompanying SAS output.
a. Use the model that includes all three independent variables (X1, X2, and X3) to answer the following questions.
(1) What is the predicted SBP for a 50-year-old smoker with a quetelet index of 3.5?
(2) What is the predicted SBP for a 50-year-old nonsmoker with a quetelet index of 3.5?
(3) For 50-year-old smokers, estimate the change in SBP corresponding to an increase in quetelet index from 3.0 to 3.5.
b. Using the computer output, determine and compare the R2-values for the three models. If you use R2 and model simplicity as the criteria for selecting a model, which of the three models appears to be the best?
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