Suppose we have a clinical data set with a response Y= concentration of LDL (bad) cholesterol in mg/dL. The data set has measurements for five predictors: X = dose of Simvastatin drug (inhibits cholesterol production) in mg/day, X2 = dose of Ezetimibe drug (decreases cholesterol absorption) in mg/day, X3 Gender (1 for female, 0 for male), X4 = Interaction between Simvastatin and Ezetimibe, and X5 Interaction between Simvastatin and Gender. We use least squares to fit a multiple regression model, and we get the following coefficient estimates: B0 = 100, = -1.25, B2 = -0.5, = -10, 4 = -0.05, 5 = 0.25.