AP Statistics : How to define control groups in an experiment

Study concepts, example questions & explanations for AP Statistics

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Example Questions

Example Question #1 : How To Conduct An Experiment

A drug company wants to test whether its medication reduces cancer risk. Assuming the company conducts an experiment in which participants are randomly assigned to treatment and control groups, what would the appropriate control group look like?

Possible Answers:

Those assigned to the control take the medication and then suddenly discontinue taking it. 

Those assigned to the control take a sugar pill. 

Those assigned to the control take the medication throughout the study period. 

Correct answer:

Those assigned to the control take a sugar pill. 

Explanation:

The only thing you want to vary across groups when you're conducting an experiment is the treatment. Since taking pills is a part of taking medication (the treatment), medical experiments often employ something called a placebo-controlled study where outcomes for those who are randomly assigned to take the medication are compared to outcomes for those who are randomly assigned to take a sugar pill. The sugar pill is expected to have no effect, so it serves as a useful baseline to compare the treatment to. 

Example Question #2 : How To Define Control Groups In An Experiment

In a public health study, researchers want to see how the addition of fresh produce stands in inner cities can affect the body weights of people who live within 1 mile of the stands.

The research group gathers data from several groups. Please identify which is the Control group.

Possible Answers:

Area A received a brand new fresh fruit and vegetable stand.

The researchers gathered information on body weight of people living within 1 mile of this area's central location, both at the starting date and ending date of the study (1 year later).

Area B received a new fresh fruit and vegetable stand.

The researchers gathered information on body weight of people living within 1 mile of this area's central location, both at the starting date and ending date of the study (1 year later).

There is no control group in this study.

There is a small town nearby which has several produce stands but also received another new fruit and vegetable stand.

The researchers gathered information on body weight of people living within 1 mile of this area's central location, both at the starting date and ending date of the study (1 year later).

One area of the city received no fresh fruit and vegetable stand.

The researchers gathered information on body weight of people living within 1 mile of this area's central location, both at the starting date and ending date of the study (1 year later).

Correct answer:

One area of the city received no fresh fruit and vegetable stand.

The researchers gathered information on body weight of people living within 1 mile of this area's central location, both at the starting date and ending date of the study (1 year later).

Explanation:

Areas A and B are both experimental areas, where they received the treatment (the new produce stand), so comparing body weights before and after the treatment will provide valuable data.

 

The area of the city which did not receive the treatment (a produce stand) will provide data of how body weight may change over time naturally, without the stand, in order to compare the effects of the stands elsewhere.

 

The nearby town already has produce stands and provides residents with a different food environment, so it cannot act as the control group. It has different conditions than the experimental areas A and B, so comparing it to these areas will not provide helpful data in terms of the treatment's effects.

Example Question #3 : Data Collection

You and your classmate want to test the effect of food coloring on plant color. One of the groups in the experiment receives dye-free water. Which group is this?

Possible Answers:

Experimental group

Control group

Neither

Placebo group

Correct answer:

Control group

Explanation:

The control group receives no treatment.

The experimental group receives the treatment of the independent variable.

Because the flowers getting no dye do not receive the treatment, it is the control group.

Example Question #82 : Data

You and your friend want to test the effect of different brands of fertilizer on sunflower height.

One group receives no fertilizer during the course of the experiment.

Which group is this?

Possible Answers:

Experimental group

Placebo group

Neither

Control group

Correct answer:

Control group

Explanation:

The control group receives no treatment.

The experimental group receives the treatment of the independent variable.

Because the sunflowers getting no fertilizer do not receive the treatment, it is the control group.

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