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Ch. 1 - Introduction to Statistics
Larson - Elementary Statistics: Picturing the World 8th Edition
Larson8th EditionElementary Statistics: Picturing the WorldISBN: 9780137493470Not the one you use?Change textbook
All textbooksLarson 8th EditionCh. 1 - Introduction to StatisticsProblem 1.3.19b
Chapter 1, Problem 1.3.19b

A company wants to test the effectiveness of a new acne cream. The company recruits 500 girls ages 13 to 17 who have acne. The subjects are randomly assigned into two groups. One group is given the acne cream and the other is given a placebo that looks exactly like the acne cream. Both groups apply the cream daily for two months. Facial photos are taken at the beginning and end of the treatment to compare results.
b. Identify a potential problem with the experimental design being used and suggest a way to improve it.

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1
Identify the potential problem: The experimental design does not mention whether the study is double-blind. If participants or researchers know which group is receiving the acne cream and which is receiving the placebo, this could introduce bias in the results.
Explain the issue: If participants know they are receiving the actual acne cream, they might expect better results and report improvements due to the placebo effect. Similarly, researchers analyzing the photos might unconsciously favor the group receiving the acne cream if they are aware of the group assignments.
Suggest an improvement: To address this issue, the study should be conducted as a double-blind experiment. This means that neither the participants nor the researchers analyzing the results should know which group is receiving the acne cream and which is receiving the placebo.
Describe how to implement the improvement: Assign a third party to label the creams and manage the group assignments. This third party should not be involved in the analysis of the results. The labels should only be revealed after the data has been collected and analyzed.
Explain the benefit of the improvement: Conducting the study as a double-blind experiment reduces bias and ensures that the results are more reliable and valid, providing a clearer understanding of the acne cream's effectiveness.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Random Assignment

Random assignment is a technique used in experimental design to ensure that each participant has an equal chance of being placed in any group. This helps to eliminate selection bias and ensures that the groups are comparable at the start of the experiment. In this case, random assignment is crucial for determining whether the observed effects on acne are due to the cream or other factors.
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Placebo Effect

The placebo effect occurs when participants experience a perceived improvement in their condition simply because they believe they are receiving treatment, even if it is a placebo. This psychological phenomenon can confound the results of an experiment if not properly controlled. In the acne cream study, the use of a placebo is intended to account for this effect, but it must be carefully monitored to ensure valid conclusions.
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Control Group

A control group is a baseline group that does not receive the experimental treatment, allowing researchers to compare outcomes against those who do. In this study, the group receiving the placebo serves as the control group. Identifying issues with the control group, such as ensuring it is adequately blinded, is essential for validating the effectiveness of the acne cream and minimizing bias in the results.
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Related Practice
Textbook Question

A company wants to test the effectiveness of a new acne cream. The company recruits 500 girls ages 13 to 17 who have acne. The subjects are randomly assigned into two groups. One group is given the acne cream and the other is given a placebo that looks exactly like the acne cream. Both groups apply the cream daily for two months. Facial photos are taken at the beginning and end of the treatment to compare results.

Identify the experimental units and treatments used in this experiment.

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Textbook Question

"Researchers in Japan tested the effect of cannabidiol (CBD) in treating late teenagers with social anxiety disorder (SAD). Thirty-seven 18- to 19-year-old teenagers with SAD took part in the study. The patients were assigned at random to receive a daily dose of either CBD or a placebo for 4 weeks. Symptoms were measured using The Fear of Negative Evaluation Questionnaire and the Liebowitz Social Anxiety Scale at the beginning and end of the treatment. (Source: Frontiers in Psychology)

The experiment is described as a placebo-controlled, double-blind study. Explain what this means."

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Textbook Question

Researchers in Japan tested the effect of cannabidiol (CBD) in treating late teenagers with social anxiety disorder (SAD). Thirty-seven 18- to 19-year-old teenagers with SAD took part in the study. The patients were assigned at random to receive a daily dose of either CBD or a placebo for 4 weeks. Symptoms were measured using The Fear of Negative Evaluation Questionnaire and the Liebowitz Social Anxiety Scale at the beginning and end of the treatment. (Source: Frontiers in Psychology)

a. Identify the experimental units and treatments used in this experiment.

6
views
Textbook Question

"Researchers in Japan tested the effect of cannabidiol (CBD) in treating late teenagers with social anxiety disorder (SAD). Thirty-seven 18- to 19-year-old teenagers with SAD took part in the study. The patients were assigned at random to receive a daily dose of either CBD or a placebo for 4 weeks. Symptoms were measured using The Fear of Negative Evaluation Questionnaire and the Liebowitz Social Anxiety Scale at the beginning and end of the treatment. (Source: Frontiers in Psychology)

How could blocking be used in designing this experiment?"

Textbook Question

A company wants to test the effectiveness of a new acne cream. The company recruits 500 girls ages 13 to 17 who have acne. The subjects are randomly assigned into two groups. One group is given the acne cream and the other is given a placebo that looks exactly like the acne cream. Both groups apply the cream daily for two months. Facial photos are taken at the beginning and end of the treatment to compare results.

c. How could this experiment be designed to be double-blind?

6
views
Textbook Question

"Researchers in Japan tested the effect of cannabidiol (CBD) in treating late teenagers with social anxiety disorder (SAD). Thirty-seven 18- to 19-year-old teenagers with SAD took part in the study. The patients were assigned at random to receive a daily dose of either CBD or a placebo for 4 weeks. Symptoms were measured using The Fear of Negative Evaluation Questionnaire and the Liebowitz Social Anxiety Scale at the beginning and end of the treatment. (Source: Frontiers in Psychology)

Identify a potential problem with the experimental design being used and suggest a way to improve it."