Treating breast cancer. The most common treatment for breast cancerdiscovered in its

Chapter 0, Problem 9.26

(choose chapter or problem)

Treating breast cancer. The most common treatment for breast cancerdiscovered in its early stages was once removal of the breast. It is now usual toremove only the tumor and nearby lymph nodes, followed by radiation. To studywhether these treatments differ in their effectiveness, a medical team examinesthe records of 25 large hospitals and compares the survival times after surgery ofall women who have had either treatment.(a) What are the explanatory and response variables?(b) Explain carefully why this study is not an experiment.(c) Explain why confounding will prevent this study from discovering whichtreatment is more effective. (The current treatment was in fact recommendedafter several large randomized comparative experiments.)