Table 5.14 is from a study of nonmetastatic osteosarcoma described in the LogXact 7 manual (Cytel Software, 2005, p. 171). The response is whether the subject achieved a three-year disease-free interval.
a. Show that each predictor has a significant effect when it is used individually without the other predictors.
b. Try to fit a main-effects logistic regression model containing all three predictors. Explain why the ML estimate for the effect of lymphocytic infiltration is infinite.
c. Using conditional logistic regression, conduct an exact test of the hypothesis of no effect of lymphocytic infiltration, controlling for the other variables. Interpret.
d. Using conditional logistic regression, find a 95% confidence interval for the effect in (c). Interpret.