IMathAS-libretexts

Researchers wanted to study whether or not Botox injected under the arms can reduce sweating.

Which of these is a matched pairs design?

Randomly assign the underarms of some subjects to be injected with Botox, and those of other subjects with salt water.
For each subject, one underarm is injected with Botox, and the other with salt water.

Suppose each subject has one underarm injected with Botox, and the other with salt water. Which is the best way to make the assignment?

Inject Botox under the left arm for some participants and the right arm for others, choosing the arm randomly.
For the sake of consistency, inject all the right underarms with salt water and the left underarms with Botox.