Income levels can influence food choices. Higher incomes enable access to a wider range of foods, potentially providing a more balanced nutrient intake and more foods that may be higher in nutrients but not necessarily calories. Incomes can also indicate higher education level, which correlates with more attention to diet and lifestyle.
Income was assessed in NHANES via a series of questions designed to assess total household income. It includes income from wages, salaries, Social Security and retirement benefits, investments, and from relatives in the previous calendar year that the survey was held. As some households were unsure of their household income, they instead chose "Above $20,000." Other households did not indicate their income at all. Data for these households was left out of the calculation based on household income.
Although median US household income changed during the study years from 2003-2008, changes were not large. The median US household income between 2006 and 2010 was calculated to be $51,914 by the US Census Bureau. The three categories used on this site (less than $25,000; $25,000-$74,999 and over $75,000) therefore indicate low, average and high income categories on the continuum of US household incomes.