EXAMPLE 8.16

Confidence interval–based sample sizes for preferences of women and men. Consider the setting in Exercise 8.50, where we compared the preferences of women and men for two commercials. Suppose we want to do a study in which we perform a similar comparison using a 95% confidence interval that will have a margin of error of 0.1 or less. What should we choose for our sample size? Using m = 0.1 and z* in our formula, we have

We would include 192 women and 192 men in our study.