Which experimental design is described by the following experiment: A study is conducted to determine the effectiveness of a new facewash on acne-prone teens. 100 volunteers are selected and grouped...

Which experimental design is described by the following experiment:

A study is conducted to determine the effectiveness of a new facewash on acne-prone teens. 100 volunteers are selected and grouped into 50 pairs based on age/gender similarity. In each group, Teen 1 uses the new facewash and Teen 2 uses a placebo facewash.