Dr. Chou is conducting a clinical trial to test the effectiv…

Dr. Chou is conducting a clinical trial to test the effectiveness of two different brands of aspirin for reducing heart attacks in Americans over the age of 65. Her participants were randomly selected from the US population of individuals in this age category. She then randomly assigned them to take Brand A or Brand B. In this example, the purpose of random selection is to enhance _____, whereas the purpose of random assignment is to enhance _____.