Researchers wanted to investigate whether there is an association between television watching and heart disease. They recruited 80,000 adults and recorded how many hours of TV each person watched per week, along with other variables such as diet, amount of physical activity, and body mass index (BMI). The researchers found that people who watched more TV had a higher risk of heart disease. However, they note in the article: “Physical inactivity is strongly associated with both television watching and heart disease, and therefore is a potential source of confounding.” Which of the following best explains the meaning of the statement?
