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. Orringer et al. used in a design.
Seaton et al. used a completely design.

Blocking in a paired design

Completed randomized design

Step-by-step explanation:

Orringer et. al used blocking in a paired design. He use the special type of randomized block design; a matched pair design wherein there is just two treatment conditions (laser treatment and the sham treatment) and the subjects are then group the subjects in pairs using the blocking variable which is a treatment applied to one side of face randomly chosen.

While Seaton et. al. used a completely randomized design. Here the subjects/participants are just merely assigned albeit randomly to either the laser or the sham treatment.