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.

b. A study was conducted to examine the possible relationship between coronary disease and obesity. The study found that the proportion of obese persons having developed coronary disease was much higher than the proportion of nonobese persons. A medical researcher states that the population of obese persons generally has higher incidences of hypertension and diabetes than the population of nonobese persons.

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Drinking Status Heavy drinker Light drinker Total Lung Cancer Yes 50 2150 2200 No Total 30 2,770 2,800 80 4,920 5,000