Section 1.1 Sampling 7 Solution We start with the third car, then count by fives to determine which cars will be sampled. The sample will consist of cars numbered 3, 8, 13, 18, and so on. Voluntary response sampling Voluntary response samples are often used by the media to try to engage the audience. For example, a news commentator will invite people to log on to a website to express an opinion, or a radio announcer will invite people to call the station to say what they think. How reliable are voluntary response samples? To put it simply, voluntary response samples are never reliable. People who go to the trouble to volunteer an opinion tend to have stronger opinions than is typical of the population. In addition, people with negative opinions are often more likely to volunteer their responses than those with positive opinions. Figures 1.1–1.4 illustrate several valid methods of sampling. Figure 1.1 Simple random sampling Figure 1.2 Systematic sampling Figure 1.3 Stratified sampling Figure 1.4 Cluster sampling Check Your Understanding 3. A radio talk-show host invites listeners to send an email to express their opinions on an upcoming election. More than 10,000 emails are received. What kind of sample is this? 4. Every ten years, the U.S. Census Bureau attempts to count every person living in the United States. To check the accuracy of their count in a certain city, they draw a sample of census districts (roughly equivalent to a city block) and recount everyone in the sampled districts. What kind of sample is formed by the people who are recounted?
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