A 10-year study conducted by the American Heart Association provided data on how age, blood pressure, and smoking relate to the risk of strokes. Data from a portion of this study
follow. Risk is interpreted as the probability (times 100) that a person will have a stroke
over the next 10-year period. For the smoker variable, 1 indicates a smoker and 0 indicates
a nonsmoker.
Risk Age Blood Pressure Smoker
12 57 152 0
24 67 163 0
13 58 155 0
56 86 177 1
28 59 196 0
51 76 189 1
18 56 155 1
31 78 120 0
37 80 135 1
15 78 98 0
22 71 152 0
36 70 173 1
15 67 135 1
48 77 209 1
15 60 199 0
36 82 119 1
8 66 166 0
34 80 125 1
3 62 117 0
37 59 207 1
a. Develop an estimated regression equation that can be used to predict the risk of stroke
given the age and blood-pressure level.
b. Consider adding two independent variables to the model developed in part (a), one for
the interaction between age and blood-pressure level and the other for whether the person
is a smoker. Develop an estimated regression equation using these four independent
variables.
c. At a .05 level of significance, test to see whether the addition of the interaction term
and the smoker variable contribute significantly to the estimated regression equation
developed in part (a).