In the following descriptions of a study, confounding is present. Describe the explanatory and confounding variable in the study and how the confounding may invalidate the conclusions of the study. Furthermore, suggest how you would change the study to eliminate the effect of the confounding variable.

a. A prospective study is conducted to study the relationship between incidence of lung cancer and level of alcohol drinking. The drinking status of 5,000 subjects is determined, and the health of the subjects is then followed for 10 years. The results are given below

Lung Cancer Drinking Status Yes No Total Heavy drinker 50 2,150 2,200 Light drinker 30 2,770 2,800 Total 80 4,920 5,000