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. complete parts (a) through (c). (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 facial photos. c. the experimental units are the 500 girls ages 13 to 17 who have acne. the treatment is the new cream used to treat acne. d. the experimental unit is the new cream used to treat acne. the treatments are the two months over which the cream is applied.

Explanation:

Experimental units are the entities on which the experiment is performed. Here, 500 girls ages 13 - 17 with acne are the ones being experimented on. Treatments are what is being done to the experimental units. In this case, it's the new acne - cream (and the placebo which is a control treatment). Facial photos are for data collection, group assignments are for organizing the experiment, and the time period is for the duration of the treatment application.

Answer:

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