More coffee protects from cancer? In February 2015, a new study published in the Journal of the National Cancer Institute shows people who regularly drink coffee have a lower chance of developing skin cancer. Based on this study, individuals drinking four or more cups of coffee a day had 20 percent lower exposure rate to develop skin cancer.

a. Explain how avoiding the sun could be strongly associated both with total cups of coffee drunk in a day and with a decrease in the exposure to skin cancer and hence, could be a lurking variable responsible for the observed association between coffee and skin cancer exposure.

b. Explain how avoiding the sun could be a common cause of both variables.