As cats age, they can suffer a decline in cognitive functioning. Memory, the ability to learn, awareness, sight, and hearing can all deteriorate. A study is to be conducted to determine which of two medicines, Anipryl or a monoamine oxidase inhibitor, is more effective in promoting cognitive health and reducing the onset of feline cognitive dysfunction. Researchers will randomly select 150 cats from 10 different large veterinary practices around the country. All the cats will be more than 10 years old, and their owners have given consent to participate in the study. Changes in cognitive health will be evaluated after six months of treatment.

Part A: What would be an advantage of adding a control group to the design of the study? (2 points)

Part B: Assuming a control group is added, explain how you would assign the 150 cats to the three treatment groups for a completely randomized design. (4 points)

Part C: Rather than using a completely randomized design, one group of researchers proposes blocking on veterinary clinics whereas another group of researchers wants to block on breed of cat. How would you decide which one of these two variables to use as a blocking variable?