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Types of Sampling - 7th data & statistics

Last updated over 2 years ago
30 questions
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.

REVIEW THE VOCAB:

Types of Samples from a Population

When taking a survey, the population is the group of people about whom the information is to be gathered.  For example, if you wanted to conduct a survey about what foods to serve in the cafeteria, the population would be the entire student body.  Since it is not usually convenient to survey the total population, different kinds of samples may be used.

A representative sample is a subgroup of the population that matches the general characteristics of the entire population.  If you choose to sample 10% of the students, you would need to include an equivalent fraction of students from each grade and an equivalent ratio of male to female students as the larger population.

A convenience sample is a subgroup of the population where it is easy to collect data.  Only sampling the students in your homeroom, for example, would be convenient, but would not necessarily accurately represent the entire school.

A cluster sample is a subgroup of the population that contains a common characteristic.  Sampling only the eighth graders, in the above example, would be a cluster sample.  Again, this sample would not necessarily represent the entire school.

A voluntary response sample contains only the sample of the population that chose to respond.  This also would not necessarily represent the entire population.
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As the social director of the Class Council, Ramin would like to survey a few students about their interests.
When Ramin analyzes the results from the survey, he wants to make claims about the interests of all of the students in his 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 Ramin 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?

1

As the social director of the Class Council, Ramin would like to survey a few students about their interests.
When Ramin analyzes the results from the survey, he wants to make claims about the interests of all of the students in his 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 all of his friends at school?  Why or why not?

1

As the social director of the Class Council, Ramin would like to survey a few students about their interests.
When Ramin analyzes the results from the survey, he wants to make claims about the interests of all of the students in his 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?

There are a variety of ways to choose samples of the population you are studying. 
Every sample has features that make it more or less representative of the larger population. 

For example, if you want to represent all of the students at your school, but you survey all of the students at school 30 minutes after the last class has ended, you are likely to get a disproportionate number of students who play school sports, attend after-school activities, or go to after-school tutoring.
1

If you ask the opinion of the people around you, then you have used a convenience sample.

Would you expect a convenience sample to represent the entire student population at your school?  Why or why not?

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If you email or create an online questionnaire then you have used a voluntary response sample. 

What are some features of the people in a volunteer response sample?  Could it represent the sample of all of the students at school accurately?

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You use a cluster sample if you first divide the students into smaller groups so that each of the smaller groups represents all of the students at your school.  Then you randomly select one or more of these groups to sample. 

How might you divide the students at your school into groups that each represent the whole school?  Explain. 

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Are there any reasons that these clusters might not be fully representative of all the students at your school?

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

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

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

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

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

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

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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.
  1. Can you legitimately conclude from this study that teenagers who play violent video games tend to be more aggressive?  Why or why not?

1

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.

2. 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?

1

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.

3. 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?

1

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.

4. 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?

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What type of sample is this?

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Will this generate valid inferences? Explain

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What type of sample is this?

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Will this generate valid inferences? Explain

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What would be a convience sample for this situation?

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What would be a voluntary response sample?

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Discuss why the samples you described may not generate valid inferences

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"The first 20 people in line for the matinne"
Which type of sample is this?

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"Adults at the movie theater"
Which type of sample is this?

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"People who agree to fill out your survey"
Which type of sample is this?

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Is this a representative sample? Explain

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What should the principal do?

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Which is an example of unbiased sampling?