Question

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 experiment design.

B). What is the advantage and disadvantage of Oriinger's method?

Answer 1

a)

Seaton - used randomized design

Orringer - used blocking in a paired design

b)

paired design is also called matched-subjects design

and randomized design is called with-subjects

Strengths and weaknesses of matched-subjects design

Within-subjects and matched-subjects designs have similar strengths, but different weaknesses. Both have good sensitivity to small differences between conditions because the groups are equivalent (or even identical). Therefore, smaller numbers of participants are needed. An advantage of the matched-subjects design over the within-subjects design is that there are no problems resulting from practice and carry-over effects. Therefore, procedures such as counterbalancing are not needed. The most obvious disadvantage of the matched-subjects design is that it requires a good deal of effort to match participants. Also, the requirements of matching might eliminate many potential participants because suitable matches cannot be found for them. In such cases we may be better off using a large group of randomly assigned participants in a between-subjects design.