5.23 Table 5.13 refers to the effectiveness of immediately injected or 11 2 -hourdelayed penicillin in protecting rabbits against lethal injection with

β-hemolytic streptococci.

a. LetX = delay, Y = whether cured, andZ = penicillin level. Fit the model, logit[P(Y = 1)] = βx + βZ k , deleting an intercept term so each level of Z has its own parameter. Argue that the pattern of 0 cell counts suggests that

ˆ βZ 1

= −∞and ˆ βZ 5

=∞. What does your software report?

b. Using the logit model, conduct the likelihood-ratio test of XY conditional independence. Interpret.

c. Estimate the XY conditional odds ratio. Interpret.