Description Format Details Note Source References Examples

NHANES III data

A `data.frame`

with
*17030* observations (rows)
and *16* variables (columns).

A subset of data from the National Health and Nutrition
Examination Study (NHANES) III. Subjects age >=20 are included.

A sample of 39,695 subjects was selected, representing more
than 250 million people living in the USA. Data was collected
1988-1994.

49 pseudo strata were created with 2 pseudo-PSU's in each
stratum (primary sampling units).

This is a subset of the original dataset.

Columns are:

- SEQN
Respondent sequence number.

- SDPPSU6
Pseudo-PSU (primary sampling unit).

- SDPSTRA6
Pseudo stratum.

- WTPFHX6
Statistical weight. Range

*225.93*to*139744.9*.- HSAGEIR
Age (years).

- HSSEX
Gender (

`factor`

):- 0
female

- 1
male

- DMARACER
Race (

`factor`

):- 1
white

- 2
black

- 3
other

- BMPWTLBS
Body weight (lbs).

- BMPHTIN
Standing height (inches).

- PEPMNK1R
Average Systolic BP.

- PEPMNK5R
Average Diastolic BP.

- HAR1
Has respondent smoked >100 cigarettes in life (

`factor`

):- 1
yes

- 2
no

- HAR3
Does respondent smoke cigarettes now? (

`factor`

):- 1
yes

- 2
no

- SMOKE
Smoking (

`factor`

):- 1
never (HAR1 = 2)

- 2
>100 cigs (HAR1 = 1 & HAR3 = 2)

- 3
current (HAR1 =1 & HAR3 = 1)

- TCP
Serum cholesterol (mg/100ml).

a

- HBP
High blood pressure? (

`factor`

):- 1
yes (PEPMNK1R > 140)

- 2
no (PEPMNK1R <= 140)

Taken from:

ANALYTIC AND REPORTING GUIDELINES:
The Third National Health and Nutrition Examination Survey,
NHANES III (1988-94).

In the NHANES III, 89 survey locations were randomly divided
into 2 sets or phases, the first consisting of
44 and the other, 45
locations. One set of primary sampling units (PSUs) was allocated
to the first 3-year survey period (1988-91) and the other set to
the second 3-year period (1991-94).

Therefore, unbiased national
estimates of health and nutrition characteristics can be
independently produced for each phase as well
as for both phases
combined. Computation of national estimates from both phases
combined (i.e. total NHANES III) is the preferred option;
individual phase estimates may be highly variable. In addition,
individual phase estimates are not statistically independent.

It is also difficult to evaluate whether
differences in individual
phase estimates are real or due to methodological
differences. That is, differences may be due to changes
in sampling methods or data
collection methodology over time.
At this time, there is no valid
statistical test for examining differences between phase 1 and
phase 2.

NHANES III is based on a complex multistage probability sample
design. Several aspects of the NHANES design must be taken into
account in data analysis, including the sampling weights and the
complex survey design. Appropriate sampling weights are needed to
estimate prevalence, means, medians, and other statistics.
Sampling weights are used to produce correct population estimates
because each sample person does not have an equal probability of
selection. The sampling weights incorporate the differential
3 probabilities of selection and include
adjustments for noncoverage
and nonresponse.

With the large
oversampling of young children, older persons, black persons, and
Mexican Americans in NHANES III, it is essential that
the sampling
weights be used in all analyses. Otherwise, misinterpretation of
results is highly likely.

Other aspects of the design that must be
taken into account in data analyses are the strata
and PSU pairings
from the sample design. These pairings should be used to estimate
variances and test for statistical significance.

For weighted analyses, analysts can use special computer
software packages that
use an appropriate method for estimating variances for complex
samples such as SUDAAN (Shah 1995) and WesVarPC (Westat 1996).

Although initial exploratory analyses may be performed on
unweighted data with standard
statistical packages assuming simple
random sampling, final analyses should be done on weighted data
using appropriate sampling weights.

**H&L 2nd ed.** Page 215. Table 6.3.

National Center for Health Statistics (US) and others 1996.
NHANES III reference manuals and reports.
*National Center for Health Statistics*.
CDC (free)

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