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with the Armed Forces (although their dependents are
included), incarcerated persons, and U.S. nationals living in
foreign countries.
Methodology. NHIS is a cross-sectional household interview
survey. Sampling and interviewing are continuous
throughout each year. The sampling plan follows a
multistage area probability design that permits the
representative sampling of households. Traditionally, the
sample for NHIS is redesigned and redrawn about every
10 years to better measure the changing U.S. population and
to meet new survey objectives. A new sample design was
implemented in the 2006 survey. The fundamental structure
of the 2006 design is very similar to the previous design for
the 1995–2005 surveys. Only the current sampling plan
covering design years 2006–2015 is addressed here. The first
stage of the current sampling plan consists of a sample of
428 primary sampling units (PSUs) drawn from approximately
1,900 geographically defined PSUs that cover the
50 states and D.C. A PSU consists of a county, a small group
of contiguous counties, or a metropolitan statistical area.
Within a PSU, two types of second-stage units are used: area
segments and permit segments. Area segments are defined
geographically and contain an expected 8, 12, or 16
addresses. Permit segments cover housing units built after
the 2000 census. The permit segments are defined using
updated lists of building permits issued in the PSU since
2000 and contain an expected four addresses. Within each
segment, all occupied households at the sample addresses
are targeted for interview.
The total NHIS sample of PSUs is subdivided into four
separate panels, or subdesigns, such that each panel is a
representative sample of the U.S. population. This design
feature has a number of advantages, including flexibility for
the total sample size. The households selected for interview
each week in NHIS are a probability sample representative of
the target population.
Oversampling of the black and Hispanic populations was
retained in the 2006–2015 design to allow for more precise
estimation of health characteristics in these populations. The
current sample design also oversamples the Asian
population. In addition, the sample adult selection process
was revised so that when black, Hispanic, or Asian persons
aged 65 and over are present, they have an increased
chance of being selected as the sample adult.
The current NHIS questionnaire, implemented in 1997, has
two basic parts: a Basic Module or Core and one or more
supplements that vary by year. The Core remains largely
unchanged from year to year and allows for trend analysis
and for data from more than 1 year to be pooled to increase
the sample size for analytic purposes. The Core contains
three components: the Family, the Sample Adult, and the
Sample Child. The Family component collects information
on everyone in the family. From each family in NHIS, one
sample adult and for families with children under age 18,
one sample child are randomly selected to participate in the
Sample Adult and Sample Child questionnaires. For children,
information is provided by a knowledgeable family member
aged 18 or over residing in the household. Because some
health issues are different for children and adults, these two
questionnaires differ in some items, but both collect basic
information on health status, use of health care services,
health conditions, and health behaviors.
Sample Size and Response Rate. The NHIS sample size varies
from year to year. It may be reduced for budgetary reasons
or may be augmented if supplementary funding is available.
Between 1997 and 2005, the sample numbered about
100,000 persons annually, with about 30,000–36,000
persons participating in the Sample Adult and about
12,000–14,000 in the Sample Child questionnaires. In the
2006–2015 redesign, the NHIS sample was reduced by 13%
compared with the 1995–2005 design. With four sample
panels and no sample cuts or augmentations, the expected
annual NHIS sample size (completed interviews) during
survey years 2006–2010 was, on average, 37,000 households
containing about 81,000 persons.
In 2011–2013, the NHIS sample size was augmented in 32
states and D.C. The main goal of the augmentation was to
increase the number of states for which reliable state-level
estimates can be made. In 2011, the sample size was
augmented by approximately 13%; in 2012, by
approximately 21%; and in 2013, by approximately 18%.
In 2011, the sample numbered 101,875 persons, with 33,014
persons participating in the Sample Adult and 12,850 in the
Sample Child questionnaires. In 2011, the total household
response rate was 82%. The final response rate was 66% for
the Sample Adult file and 75% for the Sample Child file.
In 2012, the sample numbered 108,131 persons, with 34,525
persons participating in the Sample Adult and 13,275 in the
Sample Child questionnaires. In 2012, the total household
response rate was 78%. The final response rate was 61% for
the Sample Adult file and 70% for the Sample Child file.
In 2013, the sample numbered 104,520 persons, with 34,557
persons participating in the Sample Adult and 12,860 in the
Sample Child questionnaires. In 2013, the total household
response rate was 76%. The final response rate was 61% for
the Sample Adult file and 69% for the Sample Child file.
Issues Affecting Interpretation. In 1997, the questionnaire was
redesigned: some basic concepts were changed, and other
concepts were measured in different ways. For some
questions there was a change in the reference period. Also in
1997, the collection methodology changed from paper-andpencil
questionnaires to computer-assisted personal
interviewing (CAPI). Because of the major redesign of the
questionnaire in 1997, most NHIS trend tables in Health,
United States begin with 1997 data. Starting with Health,
United States, 2005, estimates for 2000–2002 were revised to
use 2000-based weights and differ from previous editions of
Health, United States that used 1990-based weights for those
data years. The weights available on the public-use NHIS files
for 2000–2002 are 1990-based. Data for 2003–2011 use
Health, United States, 2014 Appendix I. Data Sources 371