6.8 Table 6.17 results from a clinical trial for the treatment of small-cell lung cancer.

Patients were randomly assigned to two treatment groups. The sequential therapy administered the same combination of chemotherapeutic agents in each treatment cycle. The alternating therapy used three different combinations, alternating from cycle to cycle.

a. Fit a cumulative logit model with main effects for treatment and gender.

Interpret the estimated treatment effect.

b. Fit the model that also contains an interaction term between treatment and gender. Interpret the interaction term by showing how the estimated treatment effect varies by gender.

c. Does the interaction model give a significantly better fit?