At one hospital, 674 women were diagnosed with breast cancer. Five years later, 88% of the Caucasian women and 83% of the African American women were...

At one hospital, 674 women were diagnosed with breast cancer. Five years later, 88% of the Caucasian women and 83% of the African American women were still alive. A researcher concludes that being Caucasian causes women with breast cancer to have an increased chance of surviving five years. Since there is no random assignment and there may have been lurking variables, this conclusion is not justified. Which of the following are possible lurking variables?