The question of whether a radical mastectomy (removal of breast, chest muscles, and lymph nodes) is more effective than simple mastectomy (removal of the breast only) in prolonging the life of women with breast cancer has been debated intensely. To study this question, a medical team examines the records of five large hospitals and compares the survival times of all women who have had either operation. a) Explain carefully why this study is not an experiment. b) If an experiment could be performed, what would be the experimental units, the explanatory independent variable (or factor), and the response dependent variable? c) Briefly outline a design for such an experiment. Think in terms of a treatment group and a control group. How do you place subjects into the two groups? d) Can you identify any ethical issues with your randomized comparison design?