Suppose the product term HT X AGE X SEX is added to the model described in Exercise 3. Is this new model still hierarchically well formulated? If so, state why; if not, state why not.

Suppose for the model described in Exercise 4 that a Wald test is carried out for the significance of the three-factor product term HT AGE SEX. Explain what is meant by the statement that the test result depends on the coding of the variable HT. Should such a test be carried out? Explain briefly.

Suppose for the model described in Exercise 3 that a Wald test is carried out for the significance of the twofactor product term HT X AGE. Is this test dependent on coding? Explain briefly.

7. Suppose for the model described in Exercise 3 that a Wald test is carried out for the significance of the main effect term AGE. Why is this test inappropriate here?

8. Using the model of Exercise 3, describe briefly the hierarchical backward elimination procedure for determining the best model.