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

Yes, the study described uses a completely randomized design because subjects are assigned to either the treatment or the placebo group purely by chance through a coin flip, which is answer D.

Step-by-step explanation:

The question you are asking about is whether the procedure used in the poison ivy cream study describes a completely randomized design. In a completely randomized experimental design, subjects are randomly assigned to different treatment groups, with one group receiving the active treatment and the other the placebo, without any other selection criteria. This is to eliminate lurking variables and ensure that the only difference between groups is the treatment itself, making it easier to attribute differences in outcomes to the treatment. Here, participants are randomly assigned to receive either the new cream or the placebo cream via coin flip, which ensures randomization. The concern regarding participants not returning is valid, but it does not invalidate the randomization process used for the initial assignment. Thus, the answer is D: Yes, the subjects are assigned to the two treatment groups completely by chance, indicating a completely randomized design.