In medical investigations, the ratio is often of more interest than the difference (e.g., individuals given treatment 1 are how many times as likely to recover as those given treatment 2?). Let . When m and n are both large, the statistic has approximately a normal distribution with approximate mean value ln(u) and approximate standard deviation .

a. Use these facts to obtain a large-sample 95% CI formula for estimating ln(u), and then a CI for u itself.

b. Return to the heart-attack data of Example 1.3, and calculate an interval of plausible values for u at the 95%

confidence level. What does this interval suggest about the efficacy of the aspirin treatment?