Table 8.12 refers to results of a clinical trial for the treatment of small-cell lung cancer. Patients were randomly assigned to two treatment groups. In the sequential therapy, the same combination of chemotherapeutic agents was administered in each treatment cycle; in the alternating therapy, three different combinations were given, alternating from cycle to cycle.

a. Fit a proportional odds model with main effects for treatment and gender. Interpret estimated effects.

b. Fit the model that also contains an interaction term between treatment and gender. Interpret. Does this model give a better fit? Show that this model is equivalent to using the four gender-treatment combinations as levels of a single explanatory factor.

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Table 8.12 Response to Chemotherapy Progressive No Partial Complete Therapy Gender Disease Change Remission Remission Sequential Male 28 45 29 26 Female 4 12 5 2 Alternating Male 41 Female 12 44 7 20 20 3 1 Source: W. Holtbrugge and M. Schumacher, Appl. Statist., 40: 249-259 (1991).