National Center for Health Statistics

Impact of the Pandemic on

National Health Interview Survey Data Collection

Stephen Blumberg

Director, Division of Health Interview Statistics

CDC/National Center for Health Statistics

2021 FCSM Research and Policy Conference

November 2, 2021
National Health Interview Survey

 Purpose: To monitor the health of the US population through the 

collection and analysis of data on a broad range of health topics

 Sample: Address-based, clustered sample of housing units from every

state, to be representative of the civilian noninstitutionalized US 

population

 Mode: In-person interviews by Census interviewers, with follow-up by 

telephone if needed

 Questionnaire: Includes sample adult and sample child sections 

 Data collection: Continuous, with quarterly and annual data files

 Sample size: Complete interviews for 27,000+ sample adults and 9,000+ 

sample children annually
2019 NHIS Questionnaire Redesign

 Improve the relevance of covered health topics, 

better meeting the needs of DHHS and other 

data users

 Harmonize overlapping content with other 

federal heath surveys

 Reduce respondent burden and improve data 

quality

 Shorten questionnaire and reduce variation in 

interview times

 Eliminate or reduce content better covered by 

other methods

 Establish a long-term structure of periodic 

content
2019 NHIS Questionnaire Redesign

 Reduced the total possible number of 

respondents from 3 to 2

• Dropped the family interview

 Shortened overall length of the interview 

from 73 minutes to 48 minutes (median)

 Eliminated use of flashcards, simplified 

answer categories

→ All of which made it easier to transition 

to a telephone survey
National Health Interview Survey and the Pandemic

 Personal visits and field listing halted on March 19

 Telephone contacts only from March 19 to June 30

– Phone numbers obtained for:

• 60% of addresses from commercial address list supplier

• 33% of addresses from internet searches and interviewer effort

– Phone contact made with 61% of addresses (April-June)
National Health Interview Survey and the Pandemic

 Personal visits and field listing halted on March 19

 Telephone contacts only from March 19 to June 30

– No impact on March response rates (~59%)

– Response rates declined in April-June (~42%)

– Respondents were older and more affluent
Sociodemographic Comparisons

2020 Q1 2020 Q2

Age group

18-29 years 13.6 11.1

65 years and over 28.8 31.5

Race/ethnicity

Hispanic 14.4 11.3

Non-Hispanic black 11.2 9.4

Non-Hispanic white 66.7 71.9

Educational attainment

Less than a HS diploma 9.5 6.7

BA/BS or higher 36.5 40.5

2020 Q1 2020 Q2

Own residence 65.1 73.1

Years at current residence

Less than one year 13.0 8.5

1 to 3 years 21.6 20.0

4 to 10 years 24.8 24.8

11 to 20 years 19.2 22.2

More than 20 years 21.4 24.5

Total family income

Less than $35,000 26.0 20.5

$100,000 or more 26.6 29.2

Estimates are weighted by the initial household base weight which is the inverse of the probability of household selection.
National Health Interview Survey and the Pandemic

 Personal visits in limited areas resumed July 1

– Resumed in all areas by September 1

 Telephone first approach

– In-person visits to follow-up on nonresponse, to deliver recruitment 

materials, and to conduct interviews when telephone numbers were 

unknown

– Response rates increased as personal visits increased
Household Response Rates and Percent of Household 

Interviews Completed In Person, by Month: NHIS 2020

0

10

20

30

40

50

60

70

80

90

100

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Percent

Monthly 

response rate

Percent completed by 

personal visit
Sample Adult Followback Survey

 In August – December 2020, NHIS attempted to recontact by phone

about 20,000 sample adults who completed interviews in 2019

– Sampling frame has known coverage properties

– About 97% of the sample adults provided a phone number in 2019
Sample Adult Followback Survey

 In August – December 2020, NHIS attempted to recontact by phone

about 20,000 sample adults who completed interviews in 2019

– Completion rate was 55%

• This denominator excludes 10% of eligible sample lost to follow-up due to insufficient contact 

information (no name), death, incarceration, or placement in institutional group quarters

– Younger adults, renters, and adults with less formal education were 

less likely to be reinterviewed

– Adults reporting excellent or very good health in 2019 and adults with 

greater use of preventive health care were more likely to be 

reinterviewed
Sample Adult Followback Survey

 In August – December 2020, NHIS attempted to recontact by phone

about 20,000 sample adults who completed interviews in 2019

– Used the same questionnaire as the 2020 NHIS

– Sample can be combined with 2020 NHIS production sample

– Data users can examine intraindividual changes in health, health care, 

and well-being from before and during the pandemic
Four Different Designs, Same Questionnaire

Number of 

Addresses

Number of Completed 

Adult Interviews

1. Normal operations

(January-March) 16,555 8,063 (25.5%)

2. Telephone only

(April-June) 16,652 5,795 (18.3%)

3. Telephone first 

(July-December) 17,419 7,297 (23.1%)

4. Sample adult followback

(August-December) 19,409 10,459 (33.1%)

Totals: 70,035 31,614 (100%)

Note: Final data files include 31,568 completed interviews after dropping 46 cases with data quality concerns.
Weighting Challenges

 How to combine and weight the four samples

Weight #1: For 2020 official statistics, with recalculated base weights

Weight #2: For longitudinal analyses using followback sample

Weight #3: For production sample if analysts combine years
Weighting Challenges

 How to incorporate additional nonresponse and calibration approaches

– Recursive partitioning models (RPM) to model response propensity for 

nonresponse adjustment with followback sample

– RPM nodes also to be used when calibrating followback sample data

– Addition of housing tenure to age, sex, race/ethnicity, and education 

when calibrating production sample

 Even after weighting adjustments, some biases remained

– Adults living alone and those in poverty are underrepresented
2020 Public Use Data File Release

 Occurred on September 30, 2021

 Three analytic files for sample adults (instead of the usual one)

– Sample Adult Interview for single-year 2020 estimates and trend 

analyses

– Sample Adult Longitudinal for analyses of data from 2019 and 2020 

for the same individuals

– Sample Adult Partial for combining data from multiple years that 

include 2019 and 2020

 Data users are strongly encouraged to read the documentation
New COVID-related Content Added in July 2020

 Doctor-diagnosed and testing-confirmed history of COVID-19 infection

 Immunosuppression

 Reduced access to care due to the pandemic

 Use of telemedicine

 Change in perceived social support

 Ability to maintain social distancing at work

 New questions on vaccine receipt and reduced taste and smell sensitivity 

following COVID-19 infection were added for 2021. 
For More Information

sblumberg@cdc.gov

https://www.cdc.gov/nchs/nhis/index.htm

https://ftp.cdc.gov/pub/Health_Statistics/NCHS/Dataset_Documentation/NHIS/

2020/nonresponse-report-508.pdf