Question

The marketing department of a sports supply store wants to estimate the percentage of adults in the town who belong to a gym.

Which statement describes a method that will help the marketing department accurately estimate this percentage?

A)Select the store’s first 20 customers every day for one week, and ask each person whether he or she belongs to a gym. Calculate the percentage of the total who say “yes.”

B)Take a random sample of adults at the local park, and ask each person whether he or she belongs to a gym. Calculate the percentage of the total who say “yes.”

C)Take a random sample of adults in the town, and ask each person whether he or she belongs to a gym. Calculate the percentage of the total who say “yes.

D)Take a random sample of the store’s adult customers, and ask what percentage of their friends belong to a gym. Calculate the mean of the responses.

Answer 1

A) If you only sample people in a sports supply store, your sample will be biased.  People in a sports supply store are more likely to be people that belong to a gym.
B) While it does not have necessarily the same amount of bias as sampling people in the sports supply store, people that go to a park are generally more likely to be people that exercise or have a gym membership.
C) Taking a random sample of people in town is a good way to get a non-biased sample.  They are not necessarily predisposed to answer your question one way or another.
D) For the same reason as choice A, this is a biased sample.

C is the best choice.