The manufacturer of exercise machines for fitness centers has designed two new elliptical machines that are meant to increase cardiovascular fitness.

The two machines are being tested on 30 volunteers at a fitness center near the company’s headquarters. The volunteers are randomly assigned to one of the machines and use it daily for two months. A measure of cardiovascular fitness is administered at the start of the experiment and again at the end. The following table contains the differences in the two scores (

After – Before) for the two machines. Note that higher scores indicate larger gains in fitness.

Machine A Machine B 0 2 5 4 1 0 8 7 6 3 2 0 2 1 5 9 9 7 4 1 1 3 2 4 8 9 6 1 4 2 5 7 5 3 5 9

(a) Write a few sentences comparing the distributions of cardiovascular fitness gains from the two elliptical machines.

(b) Which machine should be chosen if the company wants to advertise it as achieving the highest overall gain in cardiovascular fitness? Explain your reasoning.

(c) Which machine should be chosen if the company wants to advertise it as achieving the most consistent gain in cardiovascular fitness? Explain your reasoning.

(d) Give one reason why the advertising claims of the company (the scope of inference) for this experiment would be limited. Explain how the company could broaden that scope of inference.