Medical researchers want to compare the success rate of a new non invasive method for replacing heart valves using a cardiac catheter with traditional open-heart surgery. They have 40 male patients, ranging in age from 55 to 75, who need valve replacement. One of several response variables will be the percentage of blood that flows backward in the wrong direction— through the valve on each heartbeat.

a. Design an experiment that uses a completely randomized design to investigate this question.

b. Design an experiment that uses a matched pairs design to investigate this question. Explain your method of pairing.

c. Which design do you prefer? Explain your answer.