Breast Cancer Advice Center

Treating Breast Cancer?

The most common treatment for breast cancer discovered in its early stages was once removal of the breast. It is now usual to remove only the tumor and nearby lymph nodes, followed by radiation. To study whether these treatments differ in their effectiveness, a medical team examines the records of 25 large hospitals and compares the survival times after surgery of all 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 which treatment is more effective. (The current treatment was in fact recommended after several large randomized comparative experiments.)

Public Comments

1. a) Explanatory variable: the type of treatment they had
   Response variable: the survival times after surgery
   
   b) The study was not an experiment because the patients in the study were not randomly assigned to receive one of the treatments by the researchers. Instead, they simple observed the outcomes, making this an observational study.
   
   c) Confounding variables will prevent this study from discovering which treatment is more effective because the patients response to treatment can be effected by a number of different factors, such as the strength of their immune system, the way they were treated after surgery etc.