Consider the highway speed limit data introduced in Exercise 10-88. Find a 99% CI on the difference in the two proportions using the alternate CI procedure described in this section. Compare the lengths of the CI from Exercise 10-88 with these in this one. Discuss the possible causes of any differences that you observe.

Exercise 10-88

A random sample of 500 adult residents of Maricopa County indicated that 385 were in favor of increasing the highway speed limit to 75 mph, and another sample of 400 adult residents of Pima County indicated that 267 were in favor of the increased speed limit.