If you want to know what a bowl of soup tastes like, do you need to eat all of the soup in the bowl?  Or can you get a good idea of the taste by trying a small sample?  When you conduct a survey, it is not usually possible for you to survey every person in the population you are interested in, such as all female teenage shoppers or all of the students at your school.  Instead, statisticians collect information about a sample (a portion) of the population.  However, finding a representative sample (a sample that represents the whole population well) is not easy.

8-29. As the social director of the 8-29. As the social director of the Class Council, Heather would like to survey a few students about their interests.  When Heather analyzes the results from the survey, she wants to make claims about the interests of all of the students in her school. If he were to survey only students on the Class Council, for example, it might be hard to make claims about what all students think. Students who are on the Class Council may not have the same social interests as other students. Consider this idea as you think about the samples described below. If Heather wanted to generalize the opinions of all students at his school, would it make sense to go to the grocery store and survey the people there?  Why or why not?   

8-29. As the social director of the 8-29. As the social director of the Class Council, Heather would like to survey a few students about their interests.  When Heather analyzes the results from the survey, she wants to make claims about the interests of all of the students in her school. If he were to survey only students on the Class Council, for example, it might be hard to make claims about what all students think. Students who are on the Class Council may not have the same social interests as other students. Consider this idea as you think about the samples described below. If she wanted to generalize the opinions of all students at her school, would it make sense to ask all of her friends at school?  Why or why not?  

8-29. As the social director of the 8-29. As the social director of the Class Council, Heather would like to survey a few students about their interests.  When Heather analyzes the results from the survey, she wants to make claims about the interests of all of the students in her school. If he were to survey only students on the Class Council, for example, it might be hard to make claims about what all students think. Students who are on the Class Council may not have the same social interests as other students. Consider this idea as you think about the samples described below. If he wanted to generalize the opinions of all students at his school, would it make sense to ask every third person who entered the cafeteria at lunch?  Why or why not?  

8-31. From what population is each of these samples taken 8-31. From what population is each of these samples taken?  Write down the actual population for each of these sampling techniques.

8-32. A study at the University of Iowa in 2008 concluded that children that play violent video games are more aggressive in real life.  Children ages 9 to 12 were studied to determine how much they played violent video games; peers and teachers were asked how much these students hit, kicked, and got into fights with other students. Can you legitimately conclude from this study that teenagers who play violent video games tend to be more aggressive?  Why or why not?    

8-32. A study at the University of Iowa in 2008 concluded that children that play violent video games are more aggressive in real life.  Children ages 9 to 12 were studied to determine how much they played violent video games; peers and teachers were asked how much these students hit, kicked, and got into fights with other students. Can you legitimately conclude from this study that children ages 9 to 12 who play violent video games are more likely to commit violent crimes?  Why or why not?   

8-32. A study at the University of Iowa in 2008 concluded that children that play violent video games are more aggressive in real life.  Children ages 9 to 12 were studied to determine how much they played violent video games; peers and teachers were asked how much these students hit, kicked, and got into fights with other students.   Can you legitimately conclude from this study that children ages 9 to 12 who play violent video games tend to hit and kick more in school? 

8-32. A study at the University of Iowa in 2008 concluded that children that play violent video games are more aggressive in real life.  Children ages 9 to 12 were studied to determine how much they played violent video games; peers and teachers were asked how much these students hit, kicked, and got into fights with other students. Can you legitimately conclude from this study that playing a lot of violent video games will cause 9 to 12-year-old students to become more violent at school?  

Practice Determine if each sample is valid. If it is not, give a suggestion to make it valid. A marketing person for a company that manufactures roller coaster reports that 92% of Americans like to ride roller coasters. She based this on the data collected from a survey that was given to people who visited American amusement parks over the course of the summer. The school newspaper reports that 47% of seventh graders at the school have at least two siblings. This is based on data that a student gathered from his 3rd period class.

Practice 3. Give at least one pro and one con for each sampling method. Then state which method is best. Snacks Stat! is considering introducing a new chip, Seeds ‘n’ Stuff. Your Manager of Surveys has suggested the following four methods for selecting a sample to determine customer demand for this product in the town of 1,500 people: Method A: Survey the first 25 people in line on a weekday for the noon showing of Monster Mayhem at the local movie theater. Method B: Survey every 5th person arriving at the local playground on a weekday afternoon until 25 people are questioned. Method C: Randomly select 5 citizens from records at town hall. Contact each person and arrange to survey him or her. Method D: Randomly select 50 citizens from records at town hall. Contact each person and arrange to survey him or her.