71. For the data of Exercise 70 we want to compare population medians for the runs in Denver versus the runs in Phoenix.

a. Obtain a bootstrap sample of 1000 differences of medians. Check the bootstrap distribution for normality using a normal probability plot.

b. Use the standard deviation of the bootstrap distribution along with the difference of the medians in the original sample and the t critical value from Exercise 70

(a) to get a 95% con dence interval for the difference of population medians.

c. Use the bootstrap sample and the percentile method to obtain a 95% con dence interval for the difference of population medians.

d. Compare the two con dence intervals.

e. How do the results for the median compare with the results for the mean? In terms of precision

(measured by the width of the con dence interval), which gives the best results?