Family income includes wages, salaries, rents from property, interest, dividends, profits and fees from their own businesses, pensions, and help from relatives. Family income data are used in the computation of the poverty level.

For purposes of the National Health Interview Survey (NHIS) and National Health and Nutrition Examination Survey (NHANES), all people within a household related to each other by blood, marriage, or adoption constitute a family. Each member of a family is classified according to the total income of the family. Unrelated individuals are classified according to their own income.

In the NHIS (in years prior to 1997) and NHANES, family income was the total income received by members of a family (or by an unrelated individual) in the 12 months before the interview. Starting in 1997 the NHIS collected family income data for the calendar year prior to the interview (for example, 1997 family income data were based on 1996 calendar year information).

For data years 1990-96, about 16-18 percent of persons had missing data on poverty level. Missing values were imputed for family income using a sequential hot deck within matrix cells imputation approach. A detailed description of the imputation procedure as well as data files with imputed annual family income for 1990-96 are available from NCHS on CD-ROM NHIS Imputed Annual Family Income 1990-96, Series 10, Number 9A.