Consider the unlisted telephone number data in Exercise 10-101. Find 95% CIs on the difference in the proportions of unlisted telephone numbers for Phoenix and Scottsdale residents using both procedures described in this chapter. Compare the lengths of these two intervals and comment on any difference you may observe.

Exercise 10.101

A random sample of 1500 residential telephones in Phoenix in 1990 indicated that 387 of the numbers were unlisted. A random sample of 1200 telephones in the same year in Scottsdale indicated that 310 were unlisted.