college graduates generally live longer than people who dropout of high school. which of these conditions is most likely to explain these differences?

Several factors account for the longer life-expectancy of college-graduates:

More mental work and less physical work: people with college degrees mostly have jobs that do not require a lot of physical activity. Non-college graduates on the other hand, tend to work in jobs that require physical strain, for example: construction, mining, or even retail.Higher income and better medical care: most college-graduates make more money than non-college-graduates (exemptions exist). People with higher incomes can acess better medical care, and can afford more nutritious food.Less likely to smoke: research has consistently found that college graduates are less likely to smoke than non-college graduates. Smoking is very harmful to one's health and one of the leading causes of disability in the U.S.