One of the first decisions the class had to make was what kind of sampling method to use.

a. They knew that a simple random sample was the “preferred” method. With 1100 teachers in 40 different sessions, the class decided not to use an SRS. Give at least two reasons why you think they made this decision.

b. The AP® Statistics class believed that there might be systematic differences in the proportions of teachers who had tattoos based on the subject areas that they taught. What sampling method would you recommend to account for this possibility? Explain a statistical advantage of this method over an SRS.

About 1100 high school teachers attended a weeklong summer institute for teaching AP® Statistics classes. After learning of the survey described in Exercise 56, the teachers in the AP® Statistics class wondered whether the results of the tattoo survey would be similar for teachers. They designed a survey to find out. The class opted to take a random sample of 100 teachers at the institute. One of the questions on the survey was: Do you have any tattoos on your body?

(Circle one)  YES  NO

Exercise 56.

What percent of U.S. adults have one or more tattoos? The Harris Poll conducted an online survey of 2302 adults and found 29% of respondents had at least 1 tattoo. According to the published report, “Respondents for this survey were selected from among those who have agreed to participate in Harris Interactive surveys.” Explain why it would not be appropriate to use these data to construct a 95% confidence interval for the proportion of all U.S. adults who have tattoos.