A large study used records from Canada’s national health care system to compare the effectiveness of two ways to treat prostate disease. The two treatments are traditional surgery and a new method that does not require surgery. The records described many patients whose doctors had chosen what method to use. The study found that patients treated by the new method were more likely to die within 8 years.

a. Further study of the data showed that this conclusion was wrong. The extra deaths among patients who were treated with the new method could be explained by other variables. What other variables might be confounded with a doctor’s choice of surgical or nonsurgical treatment?

b. You have 300 prostate patients who are willing to serve as subjects in an experiment to compare the two methods. Write a few sentences describing a completely randomized design for this experiment.