SMAT 130B-01 – CRN: 10227: 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. Complete parts​ (a) through​ (c).

Posted: November 28th, 2022

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Part 1

​(a) Identify the experimental units and treatments used in this experiment. Choose the correct answer below.

A.

The experimental units are the 500 girls ages 13 to 17 who have acne. The treatment is the group assignments.

B.

The experimental unit is the new cream used to treat acne. The treatments are the two months over which the cream is applied.

C.

The experimental unit is the new cream used to treat acne. The treatments are the facial photos.

D.

The experimental units are the 500 girls ages 13 to 17 who have acne. The treatment is the new cream used to treat acne.

Your answer is correct.

Part 2

​(b) Identify a potential problem with the experiment design being used and suggest a way to improve it. Choose the correct answer below.

A.

Only one​ non-placebo cream was studied. To increase​ validity, use more creams of different varieties.

B.

The cream is used for two months. To increase​ validity, compare photos immediately after applying the cream.

C.

Only girls ages 13 through 17 were used. To increase​ validity, use a stratified sample.

Your answer is correct.

D.

Facial photos were used to compare results. To increase​ validity, use video recorders to compare results.

Part 3

​(c) How could this experiment be designed to be a​ double-blind?

A.

For the experiment to be​ double-blind, neither the subjects nor the company would know whether the cream works or not.

B.

For the experiment to be​ double-blind, neither the subjects nor the company would know which subjects will have facial photos taken.

C.

For the experiment to be​ double-blind, neither the subjects nor the company would know how long the subjects will be applying the cream.

D.

For the experiment to be​ double-blind, neither the subjects nor the company would know whether the subjects are receiving the acne cream or the placebo.