Questions: 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. Submit Question

The answer is the second one: For each subject, one underarm is injected with Botox, and the other with salt water.

Explanation:

1. Randomly assign the underarms of some subjects to be injected with Botox, and those of other subjects with salt water.

   • This describes a completely randomized design where different subjects receive different treatments. It does not account for individual variability between subjects, which can affect the results.

2. For each subject, one underarm is injected with Botox, and the other with salt water.

   • This describes a matched pairs design. In this design, each subject serves as their own control, which helps to account for individual differences. By comparing the effects of Botox and salt water within the same subject, researchers can more accurately determine the effect of Botox on sweating.

Summary: The matched pairs design is the second option, where each subject has one underarm injected with Botox and the other with salt water. This design helps control for individual variability and provides a more accurate comparison of the treatments.