Question

"A new cream was developed to reduce the irritation caused by poison ivy. To test the effectiveness, researchers placed an ad online asking volunteers to participate in the study, and 100 subjects replied. They are informed that one group of 50 will receive a new cream and the remaining group of 50 will receive a cream with no active ingredient. As each subject enters the study facility, the researchers flip a coin. Heads means the subject goes to room A and tails means the subject goes to room B. The subjects in room A will receive the new cream and the subjects in room B will receive the inactive cream. All subjects are exposed to poison ivy and given their cream. They are asked to return in three days and report their level of irritation.

Does this procedure describe a completely randomized design for this experiment?
A. Yes, the subjects will all be exposed to poison ivy and then apply the cream.
B. Yes, the subjects are receiving either the new cream or the inactive cream.
C. No, the subjects are asked to return in three days. It is possible that some may not return, which will introduce bias into the results.
D. Yes, the subjects are assigned to the two treatment groups completely by chance.

Answer 1

No, the procedure does not describe a completely randomized design for this experiment as it introduces the possibility of bias in the results.

Step-by-step explanation:

The procedure described in the question does not represent a completely randomized design for this experiment. The reason is that the subjects are asked to return in three days, which introduces the possibility that some subjects may not return, leading to bias in the results. A completely randomized design would involve randomly assigning subjects to the treatment groups and ensuring that all subjects follow the same procedures, including the timing of reporting their level of irritation.

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Answer 2

The presence of a potential dropout rate in the study indicates that it does not represent a completely randomized design, as the final data might not reflect an unbiased sample.

Step-by-step explanation:

The procedure described in the question does not provide a completely randomized design for the experiment to test the effectiveness of the cream that reduces irritation caused by poison ivy. Although initially it seems that random assignment is used by flipping a coin to decide who goes to room A or B, and there is a control group receiving an inactive cream which is a placebo treatment, the study may be compromised if not all subjects return after three days as instructed. This follow-up issue, leading to potential dropouts, introduces the possibility of bias because the final results could be based on unrepresentative sample data. Thus, one cannot securely attribute differences in outcomes between the two groups solely to the effect of the cream if the final samples are not equivalent to the samples at the start of the experiment.