A nutritionist wants to estimate the difference between the percentage of men and women who have high cholesterol. What sample size should be obtained if she wishes the estimate to be within 2 percentage points with 90% conﬁdence, assuming that
(a) she uses the 1994 estimates of 18.8% male and 20.5% female from the National Center for Health Statistics?
(b) she does not use any prior estimates?