Refer to Exercise 12.82.
a. Write a complete second-order model that relates E(y) to the quantitative variable.
b. Add the main effect terms for the qualitative variable (at three levels) to the model of part a.
c. Add terms to the model of part b to allow for interaction between the quantitative and qualitative independent variables.
d. Under what circumstances will the response curves of the model have the same shape but different y-intercepts?
e. Under what circumstances will the response curves of the model be parallel lines?
f. Under what circumstances will the response curves of the model be identical?
Exercise 12.82
Consider a multiple regression model for a response y, with one quantitative independent variable x1 and one qualitative variable at three levels.