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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 1.3.19a
Chapter 1, Problem 1.3.19a

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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Step 1: Define the experimental units. Experimental units are the individuals or objects on which the experiment is conducted. In this case, the experimental units are the 500 girls aged 13 to 17 who have acne.
Step 2: Identify the treatments. Treatments refer to the conditions applied to the experimental units. Here, the treatments are the acne cream and the placebo cream.
Step 3: Explain the random assignment. The subjects are randomly assigned into two groups to ensure that any differences observed are due to the treatments and not other factors. Random assignment helps eliminate bias and confounding variables.
Step 4: Describe the measurement process. Facial photos are taken at the beginning and end of the treatment period to compare the effectiveness of the acne cream versus the placebo. This provides a quantitative or qualitative basis for evaluating the results.
Step 5: Highlight the purpose of the placebo. The placebo is used to control for psychological effects, such as the placebo effect, where subjects might perceive improvement simply because they believe they are receiving treatment. This ensures the results are attributable to the acne cream itself.

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Key Concepts

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

Experimental Units

Experimental units are the smallest division of experimental material to which a treatment is applied. In this study, the experimental units are the 500 girls aged 13 to 17 who have acne. Each girl represents an individual unit that receives either the acne cream or the placebo, allowing researchers to assess the treatment's effectiveness.
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Treatments

Treatments refer to the specific conditions or interventions applied to the experimental units in an experiment. In this case, there are two treatments: one group receives the actual acne cream, while the other group receives a placebo that mimics the cream's appearance. This design helps isolate the effect of the acne cream by comparing it against a control group.

Random Assignment

Random assignment is a technique used to ensure that each experimental unit has an equal chance of being assigned to any treatment group. This method helps eliminate bias and confounding variables, making the results more reliable. In this experiment, the random assignment of the girls into the two groups (acne cream and placebo) enhances the validity of the findings regarding the cream's effectiveness.
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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.

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

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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

Determine whether the data are qualitative or quantitative, and determine the level of measurement of the data set. Explain your reasoning.

The numbers of employees at fast-food restaurants in a city are listed.

20 11 6 31 17 23 12 18 40 22 13 8 18 14 37 32 25 27 25 18

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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.

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Textbook Question

Identify the sampling technique used, and discuss potential sources of bias (if any). Explain.

Questioning teachers as they leave a faculty lounge, a researcher asks 45 of them about their teaching styles.

7
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."