2020 COVID-related NHIS Study Design Changes, Introduction of a Longitudinal Sample, and COVID-Related Content

The National Center for Health Statistics continued to field the NHIS throughout 2020 with several notable changes to data collection and questionnaire content to accommodate COVID and COVID-related nonresponse.

The National Center for Health Statistics (NCHS) fielded four separate NHIS study designs during the course of 2020:

    1) Normal, in-person data collection in quarter 1,
    2) Telephone-only in quarter 2,
    3) Telephone-first in quarters 3 and 4, and
    4) The introduction in August 2020 of a longitudinal sample while maintaining part of the original 2020 sample.

Below, we describe the study design changes at various points in 2020, describe the longitudinal and partial samples, and provide an overview of COVID-related content introduced during 2020. For additional information and updates, please refer to the NCHS website on NHIS 2020 data collection efforts.

Changes to Interviewing Procedures

NHIS data are typically collected as an in-person interview. Between mid-March and July (quarter 2), the NHIS temporarily became a telephone-only survey. While the telephone-only approach was in the field, household interview response rates dropped from 60% in calendar quarter 1 of 2020 to 42.7% in quarter 2; sample adult and sample child interview response rates fell from 57.9% to 41.1% and 57.6% to 40.1%, respectively (Dahlhamer et al., 2021). In July, a telephone-first approach was implemented in selected areas, and then rolled out in all areas in September. Under the telephone-first approach, household contacts were still attempted by telephone first, and personal visits were reserved for follow-up on nonresponse, to deliver recruitment materials, and to conduct interviews when telephone numbers were unknown. The telephone-first approach will continue for the foreseeable future.

During the time that NHIS was a telephone-only survey, survey response rates decreased from 60 to 43%. However, with the introduction of the telephone-first design, response rates have increased to 50-60%. Approximately 30% of interviews were conducted in-person in September 2020.

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Longitudinal Sample

In light of changing response rates in 2020, NCHS chose to introduce a subsample of adults who had previously participated in the NHIS with known representativeness and nearly complete telephone contact information to inform weighting and estimation techniques that were use to produce official 2020 estimates. From August to December 2020, NCHS re-contacted by telephone a "longitudinal" sample of roughly 20,000 adult respondents who completed the NHIS in 2019 and invited them to complete the 2020 NHIS questionnaire. The longitudinal sample did not include sample children. 10,415 individuals from the longitudinal sample completed the 2020 NHIS questionniare. The longitudinal data collected on this sample allows users to evaluate health, health care, and well-being from before and during the pandemic. To free up resources to field the longitudinal sample, the size of the quarter 3 and 4 samples was reduced by half. Users may link an individual in the 2020 longitudinal sample to their record in the 2019 file by linking on the person's 2020 value of NHISPIDPRVYR and the person's 2019 value of NHISPID. Please see NHISPIDPRVYR for more information. LONGWEIGHT should be used in analyses evaluating individual-level changes between 2019 and 2020 among the same adults.

Partial Sample

The "partial" sample refers to the 21,153 individuals in the original 2020 sample. It excludes the individuals in the longitudinal sample who were also in the 2019 sample. The partial sample in combination wtih the longitudinal sample encompasses all 31,568 sample adults with a 2020 record. According to the 2020 Survey Description, PARTWEIGHT is only recommended for use with the 2020 data when producing estimates based on pooled 2019 and 2020 data to increase sample size; in that case SAMPWEIGHT should be used for the 2019 records. A user might, for example, create a new weight and assign PARTWEIGHT values for 2020 and SAMPWEIGHT values for 2019. SAMPWEIGHT should still be used to produce official estimates for 2020 or to compare estimates between 2019 and 2020.

Additional COVID-related content

A set of nearly 30 questions related to COVID were added to the 2020 NHIS sample adult questionnaire starting in quarter 3. Eight COVID-related questions identical to ones fielded to sample adults were also added to the sample child questionnaire.

Table 1 lists the COVID-related questions that were added in quarter 3, 2020, and whether they were available for the sample adult and sample child. Table 2 lists questions added in quarter 3, 2020 that were not specifically COVID-related but may be of interest to researchers evaluating the impact of the pandemic on social support. These questions on social support are only available for sample adults.

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Table 1. COVID-related questions added in Quarter 3, 2020

IPUMS Variable Question ID Text Sample Adult Sample Child
CVDCANTREA CNV.0010.00.3 At any time since the start of the coronavirus pandemic, were you in treatment or supposed to receive treatment for your cancer? X
CVDCANCHG CNV.0020.00.3 Were any of your treatments for cancer changed, delayed, or cancelled because of the coronavirus pandemic? X
CVDCANOTHTR CNV.0030.00.3 As a cancer patient or cancer survivor, you may need OTHER medical care related to your cancer such as lab visits, imaging, monitoring visits, rehabilitation, physical therapy, care for side-effects, or visits with medical specialists. At any time since the start of the coronavirus pandemic, did you need any of this OTHER medical care related to your cancer? X
CVDCANOTHCHG CNV.0040.00.3 Was any of this OTHER medical care related to your cancer changed, delayed, or cancelled because of the coronavirus pandemic? X
CVDDIAG CVD.0020.00.4 Has a doctor or other health professional ever told [you/SAMPLE CHILD'S NAME] that you had or likely had coronavirus or COVID-19? X X
CVDTEST CVD.0030.00.4 Have [you/SAMPLE CHILD'S NAME] ever been tested for coronavirus or COVID-19? X X
CVDTESTRSLT CVD.0040.00.4 Did the test find that [you/SAMPLE CHILD'S NAME] had coronavirus or COVID-19? X X
CVDSYMP CVD.0050.00.4 How would you describe [your/SAMPLE CHILD'S NAME] coronavirus symptoms when they were at their worst? Would you say no symptoms, mild symptoms, moderate symptoms, or severe symptoms? X X
CVDCURJOBSD SDW.0010.00.3 Thinking about your MAIN job or business, are there currently social distancing measures in effect to help keep people apart? X
CVDWCLSDCUR SDW.0020.00.3 Currently, at your MAIN job or business, how often do you still need to work closer than 6 feet to other people? Would you say all of the time, most of the time, some of the time, or none of the time? X
CVDWCLNOSD SDW.0030.00.3 When social distancing measures were NOT in effect, how often did you need to work closer than 6 feet to other people? Would you say all of the time, most of the time, some of the time, or none of the time? X
CVDWCLOFT SDW.0040.00.3 Currently, at your MAIN job or business, how often do you need to work closer than 6 feet to other people? Would you say all of the time, most of the time, some of the time, or none of the time? X
CVDJOBSDEV SDW.0050.00.3 At any time since the start of the coronavirus pandemic, did your MAIN job or business put social distancing measures into effect? X
CVDWCLSDOF SDW.0060.00.3 When social distancing measures were in effect, how often did you need to work closer than 6 feet to other people? Would you say all of the time, most of the time, some of the time, or none of the time? X
CVDMNJOBSD12M SDW.0070.00.3 Thinking about the MAIN job you held in the past 12 months, were there ever any social distancing measures in effect while you worked there? That is, were there ever practices in place to help keep people apart? X
CVDWCLSD12M SDW.0080.00.3 When social distancing measures were in effect, how often did you still need to work closer than 6 feet to other people? Would you say all of the time, most of the time, some of the time, or none of the time? X
CVDWCLNOSD12M SDW.0090.00.3 When social distancing measures were NOT in effect, how often did you need to work closer than 6 feet to other people? Would you say all of the time, most of the time, some of the time, or none of the time? X
CVDWCLSOFT12M SDW.0100.00.3 How often did you need to work closer than 6 feet to other people? Would you say all of the time, most of the time, some of the time, or none of the time? X
CVDDLYCARE ACC.0010.00.4 Was there any time when [you/SAMPLE CHILD'S NAME] DELAYED getting medical care because of the coronavirus pandemic? X X
CVDDNGCARE ACC.0020.00.4 Was there any time when [you/SAMPLE CHILD'S NAME] needed medical care for something other than coronavirus, but DID NOT GET IT because of the coronavirus pandemic? X X
VIRAPP12M ACC.0030.00.4 In the past 12 months, have [you/SAMPLE CHILD'S NAME] had an appointment with a doctor, nurse, or other health professional by video or by phone? X X
CVDVIRAPPCVD ACC.0040.00.4 Were any of [your/SAMPLE CHILD'S NAME] appointments done by video or by phone because of reasons related to the coronavirus pandemic? X X
CVDDNGHMECARE CGR.0010.00.4 Was there any time when you needed care at home from a nurse or other health professional but DID NOT GET IT because of the coronavirus pandemic? X
CVDFAMCAR12M CGR.0020.00.4 During the past 12 months, did you receive care at home from a friend or family member? X
CVDDNGFAMCAR CGR.0030.00.4 Was there any time when you needed care at home from a friend or family member but DID NOT GET IT because of the coronavirus pandemic? X
CVDFAMCAREPR CGR.0040.00.4 Did a friend or family member provide some or all of the care that a nurse or other health professional did not provide due to the coronavirus pandemic? X
CVDJOBANYSD Recode This recode indicates whether social distancing measures are or were ever in effect at the sample adult's current or recent job. X
CVDCLSWRKSD Recode This recode indicates how often the sample adult work(ed) close to others with social distancing measures in place at work. X
CVDCLSWRKNOSD Recode This recode indicates how often sample adults work(ed) close to others when social distancing measures are not or were not in place at work. X

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Table 2. Additional Relevant Questions for Sample Adults Introduced in Quarter 3, 2020

IPUMS Variable Question ID Text
EMOSUPPORT SOS.0010.00.4 How often do you get the social and emotional support you need? Would you say always, usually, sometimes, rarely, or never?
CMPSUPPORT SOS.0020.00.4 Compared with 12 months ago, would you say that you now receive more social and emotional support, less social and emotional support, or about the same?

Additional Resources

Dahlhamer JM, Bramlett MD, Maitland A, Blumberg SJ. Preliminary Evaluation of Nonresponse Bias Due to the COVID-19 Pandemic on National Health Interview Survey Estimates, April-June 2020. Hyattsville, MD: National Center for Health Statistics. February 2021.

SHADAC. NHIS: Early Release Estimates Show Unchanged Coverage Rates during First Half of 2020, although NCHS Reports Evidence of Nonresponse Bias due to COVID-19. February 15, 2021.

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