Codes and Frequencies
POVIMP1 is a variable that includes imputed values to replace missing data for the original variable POVERTY, which reports the ratio of family income to the U.S. Census Bureau's poverty thresholds for the year in question. Income to poverty threshold status was constructed based on income and the family's size and number of children.
The income-to-poverty ratios could not be calculated in two situations: 1) for families who did not supply adequate income information (i.e., those who would only indicate that their income was above or below $20,000 and those who declined to give any income information); and 2) for families where the number of children (persons under 18) equaled the number of family members (IPUMS NHIS code 98, indicating "indefinable"). In these cases, the ratio was imputed in POVIMP1. The complementary imputation flag variable IMPOVFLAG1 indicates whether responses in POVIMP1 were reported or imputed.
Related Variables and Sources of Additional Information
POVIMP1 is the first of five variables that contain imputed values for the ratio of total family income to the poverty line. It was created as part of a set of variables that provide complete (i.e., without missing values) data on family income.
One of the purposes of NHIS data is to study relationships between income and health and to monitor health and health care for persons at different income levels. However, as the technical documentation on "Multiple Imputation of Family Income and Personal Earnings in the National Health Interview Survey: Methods and Examples" describes, non-response rates are high for questions on total family income in the previous calendar year and personal earnings from employment in the previous calendar year. For more information on the imputation methodology, see EMPSTATIMP1.
Before using the imputed income and earnings variables, researchers are strongly advised to read the NCHS documentation on imputed incom, such as 2008 Imputed Family/Personal Earnings Files.
This documentation cautions that each of the five datasets must be merged with other data from the survey to form a single completed dataset. For IHIS data users, the imputed income files have already been merged with other data from each survey year for 1997-2008, as part of the process of adding these imputed income files and variables to the IHIS database.
The NCHS documentation for the imputed income files directs that analysis of the five versions of each imputed income variable should be done separately, using methods and software that are appropriate for such survey data (for example, SAS-callable SUDAAN or SAS-callable IVEware).
Only then can estimates and standard errors be combined using the combining rules described in the aforementioned document on "Multiple Imputation of Family Income and Personal Earnings in the National Health Interview Survey." The 2008 imputed income file documentation further warns:
Examples of correct data analyses and additional information about the procedures used to create the imputed data are provided in the technical documentation referred to above.
POVIMP1 is largely comparable over time, but it is indirectly affected by changes in the response categories and methods used to probe for family income information. For 2009 forward, POVIMP1 is harmonized by the IHIS staff from the NHIS poverty ratio variable (POVRATI2) estimated to the second decimal place and for the third decimal place for 2010 (POVRATI3).
From 1997 to 2006, respondents were asked an open-ended question about their family income. Those who refused to answer or said "I don't know" were asked two follow-up questions: 1) whether the figure was above or below $20,000; and 2) which of 44 grouped income categories matched their family income.
Due to the low response rates for these follow-up questions, a new series of income follow-up questions, which used an unfolding bracket methodology, was introduced in 2007. The unfolding bracket method asked a series of closed-ended income range questions (e.g., "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 amount of the family's income.
This change resulted in a somewhat different level of detail of information on which to impute income.
- 1997-2017: All persons.
- 1997-2017 : PERWEIGHT