We know that some groups of people are healthier and even live longer than others. For example, women live longer than men. People with higher incomes are healthier and live longer than people with low incomes. So a major goal of health research today is to try to eliminate this difference in health and how long people live, to get rid of these differences between groups of people. One way to do that is to learn more about these differences and to understand the reasons for the differences in health. If we knew more, we could be able to make the changes that would improve the health of people who suffer the most from health problems. So if researchers can find out who is most affected by particular health problems and the reasons they have more health problems, they would be better able to improve care of people who need it the most. This is why researchers always ask questions about the people who are doing the surveys. For instance, researchers usually ask about race, income, education, gender. We know that many people don’t answer these questions. Sometime they leave it blank and sometime they actually give an incorrect answer, thinking that income or race, for example, doesn’t have anything to do with health. This makes it difficult for researchers to learn about differences among groups of people or to develop the most effective treatments.