Two clinical trials were designed to test the effectiveness of laser treatment for acne. Seaton et al. (2003) randomly divided participants into two groups. One group received the laser treatment, whereas the other group received a sham treatment. Orringer et al. (2004) used an alternative design in which laser treatment was applied to one side of the face, randomly chosen, and the sham treatment was applied to the other side. The number of facial lesions was the response variable.

a. Identify the main component of experimental design that differs between the two studies. Give the statistical term identifying this component in experimental design.

b. Under what circumstances would there be an advantage to using the “divided-face” design over the completely randomized (two-sample)

design?

c. Assuming that the advantage identified in part (b) is met, can you think of a disadvantage of the divided-face design?