For the National Health Interview Survey and the National Health and Nutrition Examination Survey, all people within a household who are related by blood, marriage or cohabitation, or adoption constitute a family. Each member of a family is classified according to the total income of the family. Unrelated household members are classified according to their own income.
National Health Interview Survey (NHIS)
Before 1997, family income was the total income received by members of a family (or by an unrelated individual) in the 12 months before the interview. Family income included wages, salaries, rents from property, interest, dividends, profits and fees from family members’ own businesses, pensions, and help from relatives. Starting in 1997, NHIS collects family income data for the calendar year before the interview (for example, 2015 family income data were based on calendar year 2014 information). The 1997–2006 instrument allowed the respondent to provide a specific dollar amount (up to $999,995). Any family income responses greater than $999,995 were entered as $999,996. Respondents who did not know or refused to give a dollar amount in response to this question were asked if their total combined family income for the previous year was $20,000 or more, or less than $20,000. If respondents answered this question, they were given one of two flash cards and asked to indicate which income group listed on the card best represented their family’s combined income during the previous calendar year. One flash card listed incomes that were $20,000 or more, and the other listed incomes that were less than $20,000. For the 2007–2010 NHIS, the income amount follow-up questions that had been in place since 1997 were replaced with a series of unfolding bracket questions. The unfolding bracket method asked a series of closed-ended income range questions (for example, “Is it less than $50,000?”) if the respondent did not provide an answer to the exact-income amount question. The closed-ended income range questions were constructed so that each successive question established a smaller range for the family’s income. Since the 2011 NHIS, the unfolding-bracket income questions have been further refined to improve the assignment of poverty status.
For the most recent information on the family income questions, see: Characteristics about the family and household of the Sample Adult and Sample Child. In: 2019 National Health Interview Survey (NHIS) public use data release: Survey description. 2020. Available from: https://ftp.cdc.gov/pub/Health_Statistics/NCHS/Dataset_Documentation/NHIS/2019/srvydesc-508.pdf. Also see: Pleis JR, Cohen RA. Impact of income bracketing on poverty measures used in the National Health Interview Survey’s Early Release Program: Preliminary data from the 2007 NHIS. 2007. Available from: https://www.cdc.gov/nchs/data/nhis/income.pdf.
For NHIS respondents, family income data are used in computing a poverty measure. For data years 1997–2019, about 20%–34% of people had missing data on family income (FamIncome-Table). Multiple imputation was performed to impute missing data on family income for NHIS survey years 1997 and beyond starting with Health, United States, 2004. Five sets of imputed values were created for the 1997–2018 NHIS to allow for the assessment of variability caused by imputation. Starting with the 2019 NHIS, 10 sets of imputed values are created to assess the variability more precisely. A detailed description of the multiple imputation procedure and data files for 1997 and beyond are available from: https://www.cdc.gov/nchs/nhis/data-questionnaires-documentation.htm, through the Data Release page for each survey year.
For data years 1990–1996, about 16%–18% of people had missing data on family income (FamIncome-Table). In those years, missing values were imputed for family income using a sequential hot-deck, within-matrix, cells-imputation approach. A detailed description of the imputation procedure and data files, with imputed annual family income for 1990–1996, is available from: https://ftp.cdc.gov/pub/health_Statistics/nchs/Datasets/NHIS/1990-96_Family_Income/. (Also see Sources and Definitions, Poverty.)
National Immunization Surveys (NIS)
Before 1998, family income was the total income received by all family members in the 12 months before the interview. Starting in 1998, the NIS questions on family income collect data on income received by all family members for the calendar year before the interview year for households with age-eligible children, similar to NHIS. Family income is the combined total income received by all members of a family before taxes. For the family income questions, the household respondent is asked to include income received from jobs; Social Security; retirement income; unemployment payments; public assistance; interest; dividends; net income from business, farm, or rent; or any other sources. Respondents who answer “don’t know” or refuse to give a dollar amount for the total family income are asked a cascading sequence of income questions—for a total of 15 such questions—that attempt to place the family income into 1 of 15 income intervals ranging from $7,500 or less to $75,000 or more. The initial question asks if the family income for the previous year was more or less than $20,000. Subsequent sets of income range questions are asked so that each successive question establishes a narrower income range.
A family income variable is constructed from the total family income question and the cascading income questions. If an exact income is given, family income is set to this amount; otherwise, it is set to the midpoint of the tightest bounds established by the cascading income questions. The values of total family income are used to calculate an income-to-poverty ratio. For NIS, this ratio is calculated only for households with age-eligible children, using either the actual family income value or the midpoint of the interval from the series of cascading questions in the numerator and the poverty threshold provided by the U.S. Census Bureau for family size and number of related children in the household in the denominator. Details of the income questions and computation of the income-to-poverty ratio for each data collection year can be found in the NIS data documentation (“Data User’s Guide” and “Household Interview Questionnaire” for NIS–Child and NIS–Teen), available from: https://www.cdc.gov/vaccines/imz-managers/nis/data-tables.html.
For more information, see: Battaglia MP, Hoaglin DC, Izrael D, Khare M, Mokdad A. Improving income imputation by using partial income information and ecological variables. In: Proceedings of the American Statistical Association, Survey Research Methods Section. New York, NY. 2002. Available from: https://www.cdc.gov/nchs/data/nis/estimation_weighting/Battaglia2002.pdf.
FamIncome-Table. Imputed family income percentages in National Health Interview Survey, by age (years) and sex: United States, 1990–2019
|All ages||Under 18||18 and over||Under 65||1–64||18–64||65 and over||2 and over||45 and over||18 and over||40 and over|
NOTE: Data shown are weighted percentages.
SOURCE: National Center for Health Statistics, National Health Interview Survey. See Sources and Definitions, National Health Interview Survey (NHIS).