Logistic Regression: A Self-learning Text, Third Edition (Statistics in the Health Sciences)

4. Suppose that in carrying out interaction assessment for
   the model of question 2,a chunk test for all two-way
   product terms is significant. Suppose also that upon
   further interaction testing:
   a chunk test for two-way product terms involvingF
   withPOST, OCC, PF, AGE,andGENhas aP-value
   of 0.25and
   a chunk test for two-way product terms involving
   BASEwithPOST, OCC, PF, AGE,andGENhas a
   P-value of 0.70.

Which of the following choices are “reasonable” as the next
step in the assessment of interaction? Circle as many
choices as you consider reasonable.

a. All product terms except F 3 BASE should be

dropped from the model.

b. The two-way product terms involvingFwithPOST,

OCC, PF, AGE,andGENshould be dropped from

the model and backward elimination should be car-

ried out involving the two-way product terms

involvingBASEwithPOST, OCC, PF, AGE,and

GEN.

c. The two-way product terms involvingBASEwith

POST, OCC, PF, AGE,andGENshould be dropped

from the model and backward elimination should

be carried out involving the two-way product terms

involvingFwithPOST, OCC, PF, AGE,andGEN.

d. Carry out a backward elimination of all two-way

product terms.

Note: In answering the above question, the word “reason-
able” should be interpreted in the context of the hierarchi-
cal backward elimination strategy described in this text.
Also, recall thatFandBASEare exposure variables.

5. Describe how you would test for the significance of the
   two-way product terms involvingF with POST, OCC,
   PF, AGE,andGENusing the model in question 2. In
   answering this question, make sure to state the null
   hypothesis in terms of model parameters, describe the
   formula for the test statistic, and give the distribution
   and degrees of freedom of the test statistic under the
   null hypothesis.


6. Suppose that at the end of the interaction assessment
   stage, it was determined that the variablesF 3 BASE,
   F 3 POST, andBASE 3 OCCneed to remain in the
   model as significant interaction effects. Based on the
   hierarchical backward elimination strategy described
   in Chap. 7, whatVvariables are eligible to be dropped

Test 295