5.28 We expect two proportions to be about 0.20 and 0.30, and we want an 80% chance of detecting a difference between them using a 90% confidence interval.

a. Assuming equal sample sizes, how large should they be?

b. Compare the results with the sample sizes required for (i) a 90% interval with power 90%, (ii) a 95% interval with power 80%, and (iii) a 95%

interval with power 90%.