A new cream was developed to reduce the irritation caused by poison ivy. To test the effectiveness, researchers placed an ad online asking for volunteers to participate in the study. One hundred subjects replied and were informed that one group would receive the new cream and the other group would receive a cream with no active ingredient. All 100 subjects were exposed to poison ivy. Fifty were then randomly assigned to the group with the new cream, and 50 were randomly assigned to the group with the cream with no active ingredient. After three days, the subjects’ level of irritation was measured.
Answer
A
The overall level of irritation can be compared to see if the new cream had a significant effect.
B
The level of irritation for both groups can be compared to see if the new cream had a significant effect.
C
The level of irritation in the treatment group only can be compared to see if the new cream had a significant effect
D
Since one group received a cream with no active ingredient, the researchers will not be able to determine of the new cream is effective.
Explanation
Compare the irritation levels of the two groups after three days: one received the active cream, and the other received a cream with no active ingredient. Because subjects were randomly assigned, differences between the groups can be used to assess whether the new cream affected irritation. The placebo group provides a comparison, so choice B, comparing both groups, is correct.
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