2019 NHIS Redesign
The content and structure of the NHIS were substantially redesigned in 2019. The stated goals of the redesign articulated by the National Centers for Health Statistics (NCHS), the federal statistical agency that collects the NHIS, were to "reduce respondent burden by shortening the length of the questionnaire, harmonize overlapping content with other federal health surveys, establish a long-term structure of ongoing and periodic topics, and incorporate advances in survey methodology and measurement" (2019 NHIS Survey Description).
Although the 2019 redesign encompassed many changes, we highlight the following four changes as the most consequential to users who wish to understand the implications of the 2019 redesign for the comparability of NHIS data across time, described below:
- Discontinuation of whole-household data collection;
- Changes in frequency and types of core content;
- Changes to procedures to create sampling weights; and
- Change in measurement of race and Hispanic origin.
1. Discontinuation of Whole-Household Data Collection
For 1997-2018, NHIS was a sample of households, with each household potentially containing multiple families. One person, the family respondent, was selected to give information about all family members. Information was collected on demographics, health status, chronic conditions, health insurance, and injuries. Interviewers then randomly selected one adult and one child per family to complete the additional "sample adult" and "sample child" interviews. The sample adult and sample child questionnaires collected more detailed information on the individual, including Body Mass Index, mental health, access to health care, health behaviors, and (for adults) sexual orientation and details about paid employment. For these years, NCHS released separate data files for households, families, family members, sample adults, and sample children. Please see our blog post for more information on NHIS data collection in 1997-2018.
The survey design dramatically changed in 2019. The NHIS remains a sample of households, but there is no longer a family respondent who answers questions about all family members. Instead, the interviewer completes a brief household rostering interview to collect basic demographic information of all people who usually live or stay in the household. The household roster also identifies the individuals belonging to the same family in the household in cases where there is more than one family residing in the household. Then, one sample adult and one sample child are selected per household to complete the sample adult and sample child questionnaires. In households containing more than one family, the sample adult and sample child may belong to different families.
In contrast to earlier years, family-level content is collected within the sample adult and/or sample child questionnaire. If the sample adult and sample child are from the same family, the family-level content is collected in whichever interview occurs first and is copied to the other data file in a post-processing step (i.e., if the sample child interview occurs first, the family-level information is later replicated on the sample adult file). Because there is no longer an entire family questionnaire, there is loss of content on family members beginning in 2019, including information on "health insurance, access to health care and utilization of select health care services, country of birth (if not US), some employment and earnings information, active duty military time periods, disability-associated conditions, and receipt of medical advice by phone" (2019 Survey Description).
2. Changes in Frequency and Types of Core Content
Annual Core Content, content paid for by NCHS and involving the same questions from year to year, and Sponsored Content, content paid for by other federal agencies, such as questions on food security or cancer screening, have long been features of the NHIS questionnaire. In 2019, NCHS introduced two additional types of core content to the NHIS questionnaire: Rotating Core Content and Emerging Content. In contrast to Annual Core Content, Rotating Core Content appears either every other year, one out of every three years, or two out of every three years. NCHS has projected Rotating Core Content through 2027 for the Sample Adult Questionnaire and the Sample Child Questionnaire. Some content that was previously collected every year transitioned to rotating content in 2019, such as measures of severe psychological distress, injuries, and occupation and industry. This content is also summarized in Table 1. Emerging Content is also sponsored by NCHS, and involves questions about emerging topics. For example, in 2019, Emerging Content includes questions about prescription opioid use and pain management, and the 2020-2022 questionnaires include Emerging Content questions about COVID-19.
|Mental Health Assessment||A||C||A||C||A||C|
|Stressful Life Events||C||C||C||C||C|
|Allergies and Other Conditions||A||C||A||C||A||C|
|Industry and Occupation||A||A||A||A||A||A|
3. Changes to Procedures to Create Sampling Weights
Sampling weights are constructed so that each person can be inflated or expanded to represent the total population of the United States. The approach for creating NHIS sampling weights changed significantly in 2019; large declines in response rates, from approximately 90% to 60% or less, required the introduction of more sophisticated adjustment techniques to better correct for nonresponse. Major differences from past approaches to nonresponse adjustment and creation of the final sampling weights include the use of multilevel models to adjust for nonresponse and raking (rather than post-stratification) to adjust weights to match population totals. For more information about the procedures to create sampling weights, please refer to the user note on sampling weights. Results of a test conducted by NCHS in 2018 and 2019 indicate that observed differences between 2018 and 2019 estimates are attributable to changes in the procedures to create sample weights, in addition to changes in the NHIS questionnaire. Based on the results of this test, IPUMS NHIS advises users not to compare pre-2019 and 2019 forward trends in the NHIS data. For more information on the findings of this test, please see our user note on the Bridge Test.
4. Changes in Measurement of Race and Hispanic origin
In 2019, NCHS introduced two important changes to the measurement of race. First, they dropped the "primary race" question. Between 1976 and 2018, NHIS collected race using the "primary race" question, in which respondents who provided more than one racial background were prompted to indicate the race that they felt best represented them (see, for example, the 2018 questionnaire). This approach to race measurement is consistent with guidelines set in 1977 by the Office of Management and Budget's (OMB) Directive 15. In 1997, OMB set out new guidelines for the collection of information on race and Hispanic origin in federal statistical systems that established several new requirements: the incorporation of two new race categories, Asian and Native Hawaiian/Other Pacific Islander; the placement of Hispanic origin questions before race questions; and allowing survey respondents to indicate belonging to more than one race group. These were fully implemented on the NHIS in 1999 and IPUMS NHIS offers an integrated version of the NHIS race measure that is compliant with the 1997 OMB standards in the variable RACENEW. Although the "primary race" question was no longer compliant with OMB guidelines on the collection of race and Hispanic origin information, NHIS continued to ask the "primary race" question through 2018 for the purpose of bridging race measures to maintain trends over time. IPUMS NHIS has integrated this measure in the variable RACEA.
Based on communications with NCHS staff, they judged that, in 2019 (20 years after the implementation of the 1997 OMB guidelines), the race bridge measures were no longer necessary to maintain trends. Furthermore, 2019 represented an optimal time to drop the race bridge measures because other major NHIS design changes introduced in 2019 would already disrupt the ability to use the NHIS to track trends between 2018 and earlier years, and 2019 and later years. Thus, beginning in 2019, NHIS no longer included the "primary race question" on the public use data and in 2020, no longer asked the question at all (see, for example, the 2020 questionnaire). For this reason, the time series represented in RACEA ends in 2018. Users who wish to use a consistent measure of race for 1999 forward should instead use RACENEW. For more information about the measurement of race and Hispanic origin on NHIS, please refer to their Special Topics page on "Race and Hispanic Origin Information."
Second, to protect confidentiality in light of adding urban-rural county classification to the public use data, NCHS substantially reduced the available detail in race and Hispanic origin variables on the public use data. In 2018, nine distinct race categories were available on the public use data, including White; Black/African-American; Alaskan Native or American Indian; Chinese; Filipino; Asian Indian; Other Asian; Primary Race Not Releasable; and Multiple Race, No Primary Race Selected. In 2019, the number of distinct race categories was reduced to six: White; Black/African American; Aleut, Alaskan Native, or American Indian; American Indian or Alaskan Native and any other group; Asian or Pacific Islander; and Other Single and Multiple Races. There was an even greater reduction in the number of reported categories for Hispanic origin: In 2018, there were nine different Hispanic origins reported within Hispanic origin, including Mexican; Mexican-American; Puerto Rican; Central or South American; and Multiple Hispanic. In 2019 there were two: Mexican/Mexican-American and Other Hispanic. More detailed categories of race and Hispanic origin are available on the restricted use NHIS data (see the restricted use codebook).