You find a survey of the population that includes information on people's educational attainment as well as their income. you take the difference between the average income of survey respondents that went to college and the average income of survey respondents that did not go to college and arrive at $20,000. you conclude that going to college raises a person's income by $20,000. think of a possible reason that your conclusion is inappropriate. (e. g. people choosing to go to college may have a stronger support system than those that do not choose to go to college, and support systems also influence a person's future income).