13.2 A clinical trial is carried out for a new cholesterol-lowering drug. The drug is given to 500 patients, and a placebo is given to another 500 patients, using random assignment of the patients. How would you estimate the treatment effect of the drug? Suppose that you had data on the weight, age, and gender of each patient. Could you use these data to improve your estimate? Explain. Suppose that you had data on the cholesterol levels of each patient before he or she entered the experiment. Could you use these data to improve your estimate? Explain.