AP Statistics : How to identify the placebo effect in an experiment

Study concepts, example questions & explanations for AP Statistics

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Example Questions

Example Question #95 : Data

A study is trying to determine if a particular medication (Y) is effective in weight loss. Patients participating in the study were randomly assigned to groups A, B, C, D, or E. Group A will receive one dose of Y, Group B will receive two doses of Y, Group C will receive three doses of Y, Group D will receive four doses of Y, and Group E will serve as the control group. 

Which group will be receiving the placebo (a sugar pill)? 

Possible Answers:

Group B

Group A

Group E

Group D

Group C

Correct answer:

Group E

Explanation:

The control group in an experiment typically receives placebo treatments (in this case - Group E). Since all of the other groups are receiving at least one dose of the medication, they are considered to be experimental groups. 

Example Question #1 : How To Identify The Placebo Effect In An Experiment

To test if vitamin C actually makes people feel better, a vitamin company decides to run a 5-day study where they give one group of 100 sick participants vitamin C pills and another group of 100 sick people placebo pills, and monitored another group of 100 sick people who took no pills.  

At the end of the 5-day experiment, 90 participants in the vitamin C group reported feeling better. 30 participants in the no-pill group felt better after the 5-day period. Interestingly, 50 participants in the placebo group felt better after the 5-day period.

What could explain these numbers?

Possible Answers:

5 days is too long for the experiment.

Vitamin C actually makes people feel sicker.

There is no logical explanation.

The placebo effect: some participants in the placebo group began to feel better because they thought they were taking something that would help them.

5 days is too short for the experiment.

Correct answer:

The placebo effect: some participants in the placebo group began to feel better because they thought they were taking something that would help them.

Explanation:

The placebo effect is when effects are seen in a group of people who did not actually receive a treatment. 

In the vitamin C group, 90 participants felt better.

Naturally (no-pill), 30 participants felt better.

With the placebo, 50 participants felt better. Since more people felt better with the placebo than with no treatment at all, it appears that some percentage of people believed that they would feel better with a pill and actually began to feel better due to the placebo effect.

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