********************************************************************************
********************************************************************************
WARNING!!! WARNING!!! WARNING!!! WARNING!!!
THIS TEXT DOCUMENT IS OVER 200 PAGES LONG!!!!!
DO NOT PRINT THE DOCUMENT UNLESS YOU ARE ABLE
TO PRINT THIS MANY PAGES ON YOUR PRINTER!
YOU ARE ADVISED TO DOWNLOAD THE DOCUMENT TO
YOUR PERSONAL COMPUTER AND THEN VIEW OR
PRINT IT FROM WITHIN A WORD PROCESSOR!!!!
SET YOUR MARGINS TO ZERO AND USE A FONT
THAT MIMICS A TEXT PRINTER.
WARNING!!! WARNING!!! WARNING!!! WARNING!!!
********************************************************************************
********************************************************************************
Third National Health and Nutrition Examination Survey
(NHANES III), 1988-94
Catalog Number 76300
NHANES III LABORATORY DATA FILE DOCUMENTATION
Ages one year and older
December 1996
Table of Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Guidelines for Data Users. . . . . . . . . . . . . . . . . . . . . . . .
Survey Description . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sample Design and Analysis Guidelines. . . . . . . . . . . . . . . . . .
Data Preparation and Processing Procedures . . . . . . . . . . . . . . .
General References . . . . . . . . . . . . . . . . . . . . . . . . . . .
NHANES III Laboratory Data
General Information . . . . . . . . . . . . . . . . . . . . . . . .
Data File Index . . . . . . . . . . . . . . . . . . . . . . . . . .
Data File Item Descriptions, Codes, Counts, and Notes . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introduction
The National Center for Health Statistics (NCHS) of the Centers for Disease
Control and Prevention (CDC) collects, analyzes, and disseminates data on
the health status of U.S. residents. The results of surveys, analyses, and
studies are made known through a number of data release mechanisms
including publications, mainframe computer data files, CD-ROMs (Search and
Retrieval Software, Statistical Export and Tabulation System (SETS)), and the
Internet (http://www.cdc.gov/nchswww/nchshome.htm).
The National Health and Nutrition Examination Survey (NHANES) is a periodic
survey conducted by NCHS. The third National Health and Nutrition
Examination Survey (NHANES III), conducted from 1988 through 1994, was the
seventh in a series of these surveys based on a complex, multi-stage sample
plan. It was designed to provide national estimates of the health and
nutritional status of the United States' civilian, noninstitutionalized
population aged two months and older.
Data from NHANES III are being released in five public release data files:
NHANES III Household Adult Data File (Catalog Number 77560)
NHANES III Household Youth Data File (Catalog Number 77550)
NHANES III Examination Data File (Catalog Number 76200)
NHANES III Laboratory Data File (Catalog Number 76300)
NHANES III Dietary Recall Data Files (Catalog Number 76700)
A table showing the location of the interview and examination components in
the five NHANES III public release data files follows.
Location of the interview and examination components in the five NHANES III
public release data files
Data File
Topic | HA | HY | EXAM | LAB | DIET |
-----------------------------------------+-----+-----+-------+-----+------+
Sample weights | X | X | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Age/race/sex | X | X | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Ethnic background | X | X | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Household composition | X | X | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Individual characteristics | X | X | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Health insurance | X | X | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Family background | X | X | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Occupation of family head | X | X | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Housing characteristics | X | X | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Family characteristics | X | X | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Orientation | X | X | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Health services | X | X | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Selected health conditions | X | X | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Diabetes questions | X | . | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
High blood pressure and | X | . | . | . | . |
cholesterol questions | | | | | |
-----------------------------------------+-----+-----+-------+-----+------+
Cardiovascular disease questions | X | . | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Musculoskeletal conditions | X | . | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Physical functioning questions | X | . | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Gallbladder disease questions | X | . | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Location of the interview and examination components in the five NHANES III
public release data files (continued)
Data File
Topic | HA | HY | EXAM | LAB | DIET |
-----------------------------------------+-----+-----+-------+-----+------+
Kidney conditions | X | . | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Respiratory and allergy questions | X | X | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Diet questions | X | . | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Food frequency | X | . | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Vision questions | X | X | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Hearing questions | X | X | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Dental care and status | X | X | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Tobacco | X | . | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Occupation | X | . | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Language usage | X | X | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Exercise | X | . | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Social support/residence | X | . | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Vitamin/mineral/medicine usage | X | X | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Blood pressure measurement | X | . | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Birth | . | X | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Infant feeding practices/diet | . | X | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Motor and social development | . | X | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Functional impairment | X | X | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
School attendance | . | X | . | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Cognitive function | . | X | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Location of the interview and examination components in the five NHANES III
public release data files (continued)
Data File
Topic | HA | HY | EXAM | LAB | DIET |
-----------------------------------------+-----+-----+-------+-----+------+
Alcohol and drug use | . | . | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Reproductive health | . | . | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Diagnostic interview schedule | . | . | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Activity | . | . | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Physician's examination | . | . | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Height and weight | . | . | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Body measurements | . | . | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Dental examination | . | . | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Allergy skin test | . | . | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Audiometry | . | . | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Tympanometry | . | . | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
WISC and WRAT | . | . | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Spirometry | . | . | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Bone densitometry | . | . | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Gallbladder ultrasonography | . | . | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Central nervous system | . | . | X | . | . |
function evaluation | | | | | |
-----------------------------------------+-----+-----+-------+-----+------+
Fundus photography | . | . | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Physical function evaluation | . | . | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Fasting questions | . | . | . | X | . |
-----------------------------------------+-----+-----+-------+-----+------+
Location of the interview and examination components in the five NHANES III
public release data files (continued)
Data File
Topic | HA | HY | EXAM | LAB | DIET |
-----------------------------------------+-----+-----+-------+-----+------+
Laboratory tests on blood and urine | . | . | . | X | . |
-----------------------------------------+-----+-----+-------+-----+------+
Total nutrient intakes | . | . | X | . | . |
-----------------------------------------+-----+-----+-------+-----+------+
Individual foods | . | . | . | . | X |
-----------------------------------------+-----+-----+-------+-----+------+
Combination foods | . | . | . | . | X |
-----------------------------------------+-----+-----+-------+-----+------+
Ingredients | . | . | . | . | X |
-----------------------------------------+-----+-----+-------+-----+------+
Data File Definitions
HA - Household Adult Data File
HY - Household Youth Data File
EXAM - Examination Data File
LAB - Laboratory Data File
DIET - Dietary Recall Data Files
This document includes the documentation for the NHANES III Laboratory Data
File and also contains a general overview of the survey and the use of the
data files. The general overview includes five sections. The first
section, entitled "Guidelines for Data Users," contains important information
about the use of the data files. The second section, "Survey Description,"
is a brief overview of the survey plan and operation. The third section,
"Sample Design and Analysis Guidelines," describes some technical aspects of
the sampling plan and discusses some analytic issues particularly related to
the use of data from complex sample surveys. The "Data Preparation and
Processing Procedures" section describes the editing conventions and the
codes used to represent the data. The last and fifth section, "General
References," includes a reference list for the survey overview sections of
the document.
Public Use Data Files for the third National Health and Nutrition
Examination Survey will also be available from the National Technical
Information Service (NTIS). A list of NCHS public use data tapes available
for purchase from NTIS may be obtained from the Data Dissemination Branch at
NCHS. Information regarding a bibliography (on disk) of journal articles
citing data from all the NHANES and the availability of NHANES III data in
CD-ROM/SETS software format can be obtained from the Data Dissemination
Branch(301-436-8500) or by writing to:
Data Dissemination Branch
National Center for Health Statistics
Room 1018
6525 Belcrest Road
Hyattsville, Maryland 20782
NTIS can be contacted at:
NTIS - Computer Products Office
5285 Port Royal Road
Springfield, Virginia 22161
(703) 487-4807
Copies of all NHANES III questionnaires and data collection forms are
included in the Plan and Operation of the Third National Health and
Nutrition Examination Survey, 1988-94 (NCHS, 1994; U.S. DHHS, 1996). This
publication, along with detailed information on NHANES procedures,
interviewing, data collection, quality control techniques, survey design,
nonresponse, and sample weighting can be found on the NHANES III Reference
Manuals and Reports CD-ROM (U.S. DHHS, 1996). Information on how to order
this CD-ROM is available from the Data Dissemination Branch at NCHS at the
address and telephone number given above.
GUIDELINES FOR DATA USERS
Please refer to the following important information before analyzing data.
NHANES III Background Documents
o The Plan and Operation of the Third National Health and Nutrition
Examination Survey, 1988-94, (NCHS, 1994; U.S. DHHS, 1996) provides an
overview of the survey and includes copies of the survey forms.
o The sample design, nonresponse, and analytic guidelines documents on
the NHANES III Reference Manuals and Reports CD-ROM (U.S. DHHS, 1996)
discuss the reasons that sample weights and the complex survey design
should be taken into account when conducting any analysis.
o Instruction manuals, laboratory procedures, and other NHANES III
reference manuals on the NHANES III Reference Manuals and Reports
CD-ROM(U.S. DHHS, 1996) are also available for further information on
the details of the survey.
Analytic Data Set Preparation
o Most NHANES III survey design and demographic variables are found only
on the Adult and Youth Household Data Files. In preparing a data set
for analysis, other data files must be merged with either or both of
these files to obtain many important analytic variables.
o All of the NHANES III public use data files are linked with the common
survey participant identification number (SEQN). Merging information
from multiple NHANES III data files using this variable ensures that
the appropriate information for each survey participant is linked
correctly.
o NHANES III public use data files do not have the same number of
records on each file. The Household Questionnaire Files (divided into
two files, Adult and Youth) contain more records than the Examination
Data File because not everyone who was interviewed completed the
examination. The Laboratory Data File contains data only for persons
aged one year and older. The Individual Foods Data File based on the
dietary recall has multiple records for each person rather than the one
record per sample person contained in the other data files.
o For each data file, SAS program code with standard variable names and
labels is provided as separate text files on the CD-ROM that contains
the data files. This SAS program code can be used to create a SAS
data set from the data file.
o Modifications were made to items in the questionnaires, laboratory,
and examination components over the course of the survey; as a result,
data may not be available for certain variables for the full six years.
In addition, variables may differ by phase since some changes were
implemented between phases. Users are encouraged to read the Notes
sections of this document carefully for information about changes.
o Extremely high and low values have been verified whenever possible,
and numerous consistency checks have been performed. Nonetheless, users
should examine the range and frequency of values before analyzing
data.
o Some data were not ready for release at the time of this publication
due to continued processing of the data or analysis of laboratory
specimens. A listing of those data are available in the general
information section of each data file.
o Confidential and administrative data are not being released to the
public. Additionally, some variables have been recoded to help
protect the confidentiality of the survey participants. For example,
all age-related variables were recoded to 90+ years for persons who were
90 years of age and older.
o Some variable names may differ from those used in the Phase 1 NHANES
III Provisional Data Release and some variables included in the Phase 1
provisional release may not appear on these files.
o Although the data files have been edited carefully, errors may be
detected. Please notify NCHS staff (301-436-8500) of any errors in
the data file or the documentation.
Analytic Considerations
o NHANES III (1988-94) was designed so that the survey's first three
years, 1988-91, its last three years, 1991-94, and the entire six
years were national probability samples. Analysts are encouraged to use
all six years of survey results.
o Sample weights are available for analyzing NHANES III data. One of
the following three sample weights will be appropriate for nearly all
analyses: interviewed sample final weight (WTPFQX6), examined sample
final weight (WTPFEX6), and mobile examination center (MEC)- and
home-examined sample final weight (WTPFHX6). Choosing which of these
sample weights to use in any analysis depends on the variables being
used. A good rule of thumb is to use "the least common denominator"
approach. In this approach, the user checks the variables of
interest. The variable that was collected on the smallest number of
persons is the "least common denominator," and the sample weight that
applies to that variable is the appropriate one to use for that
analysis. For more detailed information, see the Analytic and Reporting
Guidelines for NHANES III (U.S. DHHS, 1996).
Referencing or Citing NHANES III Data
o In publications, please acknowledge NCHS as the original data source.
For instance, the reference for the NHANES III Laboratory Data File
is:
U.S. Department of Health and Human Services (DHHS). National Center
for Health Statistics. Third National Health and Nutrition
Examination Survey, 1988-1994, NHANES III Laboratory Data File (CD-ROM).
Public Use Data File Documentation Number 76200. Hyattsville, MD.:
Centers for Disease Control and Prevention, 1996. Available from
National Technical Information Service (NTIS), Springfield, VA.
Acrobat. PDF format; includes access software: Adobe Systems, Inc.
Acrobat Reader 2.1.
o Please place the acronym "NHANES III" in the titles or abstracts of
journal articles and other publications in order to facilitate the
retrieval of such materials in bibliographic searches.
SURVEY DESCRIPTION
The third National Health and Nutrition Examination Survey (NHANES III) was
the seventh in a series of large health examination surveys conducted in
the United States beginning in 1960. Three of these surveys, the National
Health Examination Surveys (NHES), were conducted in the 1960's (NCHS, 1965;
NCHS, 1967; NCHS, 1969). In 1970, an expanded nutrition component was added
to provide data with which to assess nutritional status and dietary
practices, and the name was changed to the National Health and Nutrition
Examination Survey (Miller, 1973; Engel, 1978; McDowell, 1981). A special
survey of Hispanic populations in the United States was conducted during
1982-1984 (NCHS, 1985).
The general structure of the NHANES III sample design was similar to that
of the previous NHANES. All of the surveys used complex, multi-stage,
stratified, clustered samples of civilian, noninstitutionalized
populations. NHANES III was the first NHANES without an upper age limit; in
fact, the age range for the survey was two months and older. A home
examination option was employed for the first time in order to obtain
examination data for very young children and for elderly persons who were
unable to visit the mobile examination center (MEC). The home examination
included only a subset of the components used in the full MEC examination
since it would have been difficult to collect some types of data in a home
setting. A detailed description of design specifications and copies of the
data collection forms can be found in the Plan and Operation of the Third
National Health and Nutrition Examination Survey, 1988-1994 (NCHS, 1994; U.S.
DHHS, 1996).
NHANES III was conducted from October 1988 through October 1994 in two
phases, each of which comprised a national probability sample. The first
phase was conducted from October 18, 1988, through October 24, 1991, at 44
locations. The second phase was conducted from September 20, 1991, through
October 15, 1994, at 45 different locations. In NHANES III, 39,695 persons
were selected over the six years; of those, 33,994 (86%) were interviewed
in their homes. All interviewed persons were invited to the MEC for a
medical examination. Seventy-eight percent (30,818) of the selected persons
were examined in the MEC, and an additional 493 persons were given a special,
limited examination in their homes.
Data collection began with a household interview. Several questionnaires
were administered in the household: Household Screener Questionnaire,
Family Questionnaire, Household Adult Questionnaire, and Household Youth
Questionnaire.
At the MEC, an examination was performed, and five automated questionnaires
or interviews were administered: MEC Adult Questionnaire, MEC Youth
Questionnaire, MEC Proxy Questionnaire, 24-Hour Dietary Recall, and Dietary
Food Frequency (ages 12-16 years). The health examination component
included a variety of tests and procedures. The examinee's age at the time
of the interview and other factors determined which procedures were
administered. Blood and urine specimens were obtained, and a number of tests
and measurements were performed including body measurements, spirometry,
fundus photography, x-rays, electrocardiography, allergy and glucose
tolerance tests, and ultrasonography. Measurements were taken of bone
density, hearing, and physical, cognitive, and central nervous system
functions. A physician performed a limited standardized medical examination
and a dentist performed a standardized dental examination. While some of the
blood and urine analyses were performed in the MEC laboratory, most analyses
were conducted elsewhere by contract laboratories.
A home examination was conducted for those sample persons aged 2-11 months
and aged 20 years or older who were unable to visit the mobile examination
center. The home examination consisted of an abbreviated version of the
tests and interviews performed in the MEC. Depending on age of the sample
person, the components included body measurements, blood pressure,
spirometry, venipuncture, physical function evaluation, and a questionnaire
to inquire about infant feeding, selected health conditions, cognitive
function, tobacco use, and reproductive history.
SAMPLE DESIGN AND ANALYSIS GUIDELINES
Sample Design
The general structure of the NHANES III sample design is the same as that
of the previous NHANES. Each of these surveys used a stratified, multi-stage
probability design. The major design parameters of the two previous NHANES
and the special Hispanic HANES, as well as NHANES III, have been previously
summarized (Miller, 1973; McDowell, 1981; NCHS, 1985; NCHS, 1994). The
NHANES III sample was designed to be self-weighting within a primary
sampling unit (PSU) for subdomains (age, sex, and race-ethnic groups). While
the sample was fairly close to self-weighting nationally for each of these
subdomain groups, it was not representative of the total population, which
includes institutionalized, non-civilian persons that were outside the
scope of the survey.
The NHANES III sample represented the total civilian, noninstitutionalized
population, two months of age or over, in the 50 states and the District of
Columbia of the United States. The first stage of the design consisted of
selecting a sample of 81 PSU's that were mostly individual counties. In a
few cases, adjacent counties were combined to keep PSU's above a minimum
population size. The PSU's were stratified and selected with probability
proportional to size (PPS). Thirteen large counties (strata) were chosen
with certainty (probability of one). For operational reasons, these 13
certainty PSU's were divided into 21 survey locations. After the 13
certainty strata were designated, the remaining PSU's in the United States
were grouped into 34 strata, and two PSU's were selected per stratum (68
survey locations). The selection was done with PPS and without
replacement. The NHANES III sample therefore consists of 81 PSU's or 89
locations.
The 89 locations were randomly divided into two groups, one for each phase.
The first group consisted of 44 and the other of 45 locations. One set
of PSU's was allocated to the first three-year survey period (1988-91) and
the other set to the second three-year period (1991-94). Therefore,
unbiased estimates (from the point of view of sample selection) of health and
nutrition characteristics can be independently produced for both Phase 1
and Phase 2 as well as for both phases combined.
For most of the sample, the second stage of the design consisted of area
segments composed of city or suburban blocks, combinations of blocks, or
other area segments in places where block statistics were not produced in
the 1980 Census. In the first phase of NHANES III, the area segments were
used only for a sample of persons who lived in housing units built before
1980. For units built in 1980 and later, the second stage consisted of sets
of addresses selected from building permits issued in 1980 or later. These
are referred to as "new construction segments." In the second phase, 1990
Census data and maps were used to define the area segments. Because the
second phase followed within a few years of the 1990 Census, new construction
did not account for a significant part of the sample, and the entire sample
came from the area segments.
The third stage of sample selection consisted of households and certain
types of group quarters, such as dormitories. All households and eligible
group quarters in the sample segments were listed, and a subsample was
designated for screening to identify potential sample persons. The
subsampling rates enabled production of a national, approximately
equal-probability sample of households in most of the United States with
higher rates for the geographic strata with high Mexican-American
populations. Within each geographic stratum, there was a nearly
equal-probability sample of households across all 89 stands.
Persons within the sample of households or group quarters were the fourth
stage of sample selection. All eligible members within a household were
listed, and a subsample of individuals was selected based on sex, age, and
race or ethnicity. The definitions of the sex, age, race or ethnic
classes, subsampling rates, and designation of potential sample persons
within screened households were developed to provide approximately
self-weighting samples for each subdomain within geographic strata and at the
same time to maximize the average number of sample persons per sample
household. Previous NHANES indicated that this increased the overall
participation rate. Although the exact sample sizes were not known until
data collection was completed, estimates were made. Below is a summary of
the sample sizes for the full six-year NHANES III at each stage of selection:
Number of PSU's 81
Number of stands (survey locations) 89
Number of segments 2,144
Number of households screened 93,653
Number of households with sample persons 19,528
Number of designated sample persons 39,695
Number of interviewed sample persons 33,994
Number of MEC-examined sample persons 30,818
Number of home-examined sample persons 493
More detailed information on the sample design and weighting and estimation
procedures for NHANES III can be found in the Plan and Operation of the
Third National Health and Nutrition Examination Survey, 1988-94 (NCHS, 1994;
U.S. DHHS, 1996) and in the Analytic and Reporting Guidelines: Third National
Health and Nutrition Examination Survey (NHANES III), 1988-94 (U.S. DHHS,
1996).
Analysis Guidelines
Because of the complex survey design used in NHANES III, traditional
methods of statistical analysis based on the assumption of a simple random
sample are not applicable. Detailed descriptions of this issue and possible
analytic methods for analyzing NHANES data have been described earlier (NCHS,
1985; Yetley, 1987; Landis, 1982; Delgado, 1990). Recent analytic and
reporting guidelines that should be used for most NHANES III analyses and
publications are contained in Analytic and Reporting Guidelines (U.S. DHHS,
1996). These recommendations differ slightly from those used by analysts for
previous NHANES surveys. These suggested guidelines provide a framework to
users for producing estimates that conform to the analytic design of the
survey. All users are strongly urged to review these analytic and reporting
guidelines before beginning any analyses of NHANES III data.
It is important to remember that this set of statistical guidelines is not
absolute. When conducting analyses, the analyst needs to use his/her
subject matter knowledge (including methodological issues) as well as
information about the survey design. The more one deviates from the original
analytic categories defined in the sample design, the more important it is to
evaluate the results carefully and to interpret the findings cautiously.
In NHANES III, 89 survey locations were randomly divided into two sets or
phases, the first consisting of 44 and the other of 45 locations. One set
of PSU's was allocated to the first three-year survey period (1988-91) and
the other set to the second three-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.
Therefore, although point estimates can be produced separately for each
phase, no test is available to test whether those estimates are
significantly different from each other.
NHANES III is based on a complex, multi-stage probability sample design.
Several aspects of the NHANES design must be taken into account in data
analysis, including the sample weights and the complex survey design.
Appropriate sample weights are needed to estimate prevalence, means,
medians, and other statistics. Sample weights are used to produce correct
population estimates because each sample person does not have the same
probability of selection. The sample weights incorporate the differential
probabilities of selection and include adjustments for noncoverage and
nonresponse. A detailed discussion of nonresponse adjustments and issues
related to survey coverage have been published (U.S. DHHS, 1996). With the
large oversampling of young children, older persons, black persons, and
Mexican-Americans in NHANES III, it is essential that the sample weights be
used in all analyses. Otherwise, a 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
using standard statistical packages and assuming simple random sampling,
final analyses should be done on weighted data using appropriate sample
weights. A summary of the weighting methodology and the type of sample
weights developed for NHANES III is included in Weighting and Estimation
Methodology (U.S. DHHS, 1996).
The purpose of weighting the sample data is to permit analysts to produce
estimates of statistics that would have been obtained if the entire
sampling frame (the United States) had been surveyed. Sample weights can be
considered as measures of the number of persons the particular sample
observation represents. Weighting takes into account several features of
the survey: the specific probabilities of selection for the individual
domains that were oversampled as well as nonresponse and differences between
the sample and the total U.S. population. Differences between the sample and
the population may arise due to sampling variability, differential
undercoverage in the survey among demographic groups, and possibly other
types of response errors, such as differential response rates or
misclassification errors. Sample weighting in NHANES III was used to:
1. Compensate for differential probabilities of selection among subgroups
(i.e., age-sex-race-ethnicity subdomains where persons living in
different geographic strata were sampled at different rates);
2. Reduce biases arising from the fact that nonrespondents may be
different from those who participate;
3. Bring sample data up to the dimensions of the target population
totals;
4. Compensate, to the extent possible, for inadequacies in the sampling
frame (resulting from omissions of some housing units in the listing
of area segments, omissions of persons with no fixed address, etc.); and
5. To reduce variances in the estimation procedure by using auxiliary
information that is known with a high degree of accuracy.
In NHANES III, the sample weighting was carried out in three stages. The
first stage involved the computation of weights to compensate for unequal
probabilities of selection (objective 1, above). The second stage adjusted
for nonresponse (objective 2). The third stage used poststratification of
the sample weights to Census Bureau estimates of the U.S. population to
accomplish the third, fourth, and fifth objectives simultaneously. In
NHANES III, several types of sample weights (see the sample weights table
that follows) were computed for the interviewed and examined sample and are
included in the NHANES III data file. Also, sample weights were computed
separately for Phase 1 (1988-91), Phase 2 (1991-94), and total NHANES III
(1988-94) to facilitate analysis of items collected only in Phase 1, only
in Phase 2, and over six years of the survey. Three sets of pseudo strata
and PSU pairings are provided to use with SUDAAN in variance estimation.
Since NHANES III is based on a complex, multi-stage sample design,
appropriate sample weights should be used in analyses to produce national
estimates of prevalence and associated variances while accounting for
unequal probability of selection of sample persons. For example, the final
interview weight, WTPFQX6, should be used for analysis of the items or
questions from the family or household questionnaires, and the final MEC
examination weight, WTPFEX6, should be used for analysis of the
questionnaires and measurements administered in the MEC. Furthermore, for a
combined analysis of measurements from the MEC examinations and associated
medical history questions from the household interview, the final MEC
examination weight, WTPFEX6, should be used. We recommend using SUDAAN
(Shah, 1995) to estimate statistics of interest and the associated variance.
However, one can also use other published methods for variance estimation.
Application of SUDAAN and alternative methods, such as the average design
effect approach, balance repeated replication (BRR) methods, or jackknife
methods for variance estimation, are discussed in Weighting and Estimation
Methodology (U.S. DHHS, 1996).
Appropriate Uses of the NHANES III Sample Weights
Final interview weight, WTPFQX6
Use only in conjunction with the sample interviewed at home and
with items collected during the household interview.
Final examination (MEC only) weight, WTPFEX6
Use only in conjunction with the MEC-examined sample and with
interview and examination items collected at the MEC.
Final MEC+home examination weight, WTPFHX6
Use only in conjunction with the MEC+home-examined sample and
with items collected at both the MEC and home.
Final allergy weight, WTPFALG6
Use only in conjunction with the allergy subsample and with items
collected as part of the allergy component of the exam.
Final CNS weight, WTPFCNS6
Use only in conjunction with the CNS subsample and with items
collected as part of the CNS component of the exam.
Final morning examination (MEC only) subsample weight, WTPFSD6
Use only in conjunction with the MEC-examined persons assigned to
the morning subsample and only with items collected in the MEC
exam.
Final afternoon/evening examination (MEC only) subsample weight, WTPFMD6
Use only in conjunction with the MEC-examined persons assigned to
the afternoon/evening subsample and only with items collected in
the MEC exam.
Final morning examination (MEC+home) subsample weight, WTPFHSD6
Use only in conjunction with the MEC- and home-examined persons
assigned to the morning subsample and with items collected during
the MEC and home examinations.
Final afternoon/evening examination (MEC+home) weight, WTPFHMD6
Use only in conjunction with the MEC- and home-examined persons
assigned to the afternoon/evening subsample and with items
collected during the MEC and home examinations.
DATA PREPARATION AND PROCESSING PROCEDURES
Automated data collection procedures for the survey were introduced in
NHANES III. In the mobile examination centers, data for the interview and
examination components were recorded directly onto a computerized data
collection form. With the exception of a few independently automated
systems, the system was centrally integrated. This operation allowed for
ongoing monitoring of much of the data. Before the introduction of the
computer-assisted personal interview (CAPI), the household questionnaire
data were reviewed manually by field editors and interviewers. CAPI
(1992-1994 only) questionnaires featured built-in edits to prevent entering
inconsistencies and out-of-range responses. The multi-level data
collection and quality control systems are discussed in detail in the Plan
and Operation of the Third National Health and Nutrition Examination Survey,
1988-1994 (NCHS, 1994; U.S. DHHS, 1996). All interview, laboratory, and
examination data were sent to NCHS for final processing.
Guidelines were developed that provided standards for naming variables,
filling missing values and coding conventional responses, handling missing
records, and standardizing two-part quantity/unit questionnaire variables.
NCHS staff, assisted by contract staff, developed data editing
specifications that checked data sets for valid codes, ranges, and skip
pattern consistencies and examined the consistency of values between
interrelated variables. Comments, collected in both interviews and
examination components, were reviewed and recoded when possible. Responses
to "Other" and "Specify" were recoded either to existing code categories or
to new categories. The documentation for each data set includes notes for
those variables that have been recoded and standardized and for those
variables that differ significantly from what appears in the original data
collection instrument. While the data have undergone many quality control
and editing procedures, there still may be values that appear extreme or
illogical. Values that varied considerably from what was expected were
examined by analysts who checked for comments or other responses that might
help to clarify unusual values. Generally, values were retained unless they
could not possibly be true, in which case they were changed to "Blank but
applicable." Therefore, the user must review each data set for extreme or
inconsistent values and determine the status of each value for analysis.
Several editing conventions were used in the creation of final analytic
data sets:
1. Standardized variables were created to replace all two-part
quantity/unit questions using standard conversion factors.
Standardized variables have the same name as the variable of the
two-part question with an "S" suffix. For instance, MAPF18S (Months
received WIC benefits) in the MEC Adult Questionnaire was created from
the two-part response option to question F18, "How long did you receive
benefits from the WIC program?," using the conversion factor 12 months
per year.
2. Recoded variables were created by combining responses from two or more
like variables, or by collapsing responses to create a summary
variable for the purpose of confidentiality. Recoded variables have the
original variable name with an R suffix. For example, place of birth
variable (HFA6X) in the Family Questionnaire was collapsed to a three
level response category (U.S., Mexico, Other) and renamed HFA6XR.
Generally, only the recoded variable has been included in the data file.
3. Fill values, a series of one or more digits, were used to represent
certain specific conditions or responses. Below is a list of the fill
values that were employed. Some of the fill values pertain only to
questionnaire data, although 8-fill and blank-fill values are found in
all data sets. Other fill values, not included in this list, are used
to represent component-specific conditions.
6-fills = Varies/varied. (Questionnaires only)
7-fills = Fewer than the smallest number that could be reported within
the question structure (e.g., fewer than one cigarette per day).
(Questionnaires only)
8-fills = Blank but applicable/cannot be determined. This means that
a respondent was eligible to receive the question, test, or component
but did not because of refusal, lack of time, lack of staff, loss of
data, broken vial, language barrier, unreliability, or other similar
reasons.
9-fills = Don't know. This fill was used only when a respondent did
not know the response to a question and said, "I don't know."
(Questionnaires only)
Blank fills = Inapplicable. If a respondent was not eligible for a
questionnaire, test, or component because of age, gender, or specific
reason, the variable was blank-filled. In the questionnaire, if a
respondent was not asked a question because of a skip-pattern,
variables corresponding to the question were blank-filled. For
examination or laboratory components, if a person was excluded by a
defined protocol (e.g., screening exclusion questions) and these
criteria are included in the data set, then the corresponding
variables were blank-filled for that person. For home examinees,
variables for examination components and blood tests not performed as
part of the home examination protocol were blank-filled.
4. For variables describing discrete data, codes of zero (0) were used to
mean "none," "never," or the equivalent. Value labels for which "0"
is used include: "has not had," "never regularly," "still taking," or
"never stopped using." Unless otherwise labeled, for variables
containing continuous data, "zero" means "zero.
5. Where there are logical skip patterns in the flow of the questionnaire
or examination component, the skip was indicated by placing the
variable label of the skip destination in parentheses as part of the
value label of the response generating the skip. For example, in the
Physical Function Evaluation, the variable PFPWC (in wheelchair) has a
value label, "2 No (PFPSCOOT)" that means that the next item for
persons not in a wheelchair would be represented by the variable,
PFPSCOOT.
Variable Nomenclature
A unique name was assigned to every NHANES III variable using a standard
convention. By following this naming convention, the origin of each
variable is clear, and there is no chance of overlaying similar variables
across multiple components. Variables range in length from three to eight
characters. The first two variable characters represent the topic (e.g.,
analyte, questionnaire instrument, examination component) and are listed
below alphabetically by topic. For questionnaires administered in the
household, the remainder of the variable name following the first two
characters indicates the question section and number. For example, data
for the response to the Household Adult Questionnaire question B1 are
contained in the variable HAB1. For most laboratory and examination
variables, as well as some other variables, a "P" in the third position
refers to "primary" and the remainder of the variable name is a brief
description of the item. For instance, in the Laboratory Data File,
information on the length of time the person fasted before the first blood
draw is contained in the variable PHPFAST. The variable PHPFAST was derived
as follows: characters 1-2 (PH) refer to "phlebotomy," character 3 (P)
refers to "primary," characters 4-8 (FAST) refer to an abbreviation for
"fasting."
CODE TOPIC
AT Alanine aminotransferase (from biochemistry profile)
AM Albumin (from biochemistry profile)
AP Alkaline phosphatase (from biochemistry profile)
AL Allergy skin test
AC Alpha carotene
AN Anisocytosis
AA Apolipoprotein (AI)
AB Apolipoprotein (B)
AS Aspartate aminotransferase (from biochemistry profile)
LA Atypical lymphocyte
AU Audiometry
BA Band
BO Basophil
BS Basophilic stippling
BC Beta carotene
BX Beta cryptoxanthin
BL Blast
BU Blood urea nitrogen (BUN) (from biochemistry profile)
BM Body measurements
BD Bone densitometry
C1 C-peptide (first venipuncture)
C2 C-peptide (second venipuncture)
CR C-reactive protein
UD Cadmium
CN Central nervous system function evaluation
CL Chloride (from biochemistry profile)
CO Cotinine
CE Creatinine (serum)(from biochemistry profile)
UR Creatinine (urine)
DM Demographic
DE Dental examination
MQ Diagnostic interview schedule
DR Dietary recall (total nutrient intakes)
EO Eosinophil
EP Erythrocyte protoporphyrin
FR Ferritin
FB Fibrinogen
RB Folate (RBC)
FO Folate (serum)
FH Follicle stimulating hormone (FSH)
FP Fundus photography
CODE TOPIC
GG Gamma glutamyl transferase (GGT) (from biochemistry profile)
GU Gallbladder ultrasonography
GB Globulin (from biochemistry profile)
G1 Glucose (first venipuncture)
G2 Glucose (second venipuncture)
SG Glucose (from biochemistry profile)
GH Glycated hemoglobin
GR Granulocyte
C3 HCO3 (Bicarbonate)(from biochemistry profile)
HD HDL cholesterol
HP Helicobacter pylori antibody
HT Hematocrit
HG Hemoglobin
AH Hepatitis A antibody (HAV)
HB Hepatitis B core antibody (anti-HBc)
SS Hepatitis B surface antibody (anti-HBs)
SA Hepatitis B surface antigen (HBsAg)
HC Hepatitis C antibody (HCV)
DH Hepatitis D antibody (HDV)
H1 Herpes 1 antibody
H2 Herpes 2 antibody
HX Home examination (general)
HF Household family questionnaire
HA Household adult questionnaire
HQ Household questionnaire variables (composite)
HS Household screener questionnaire
HY Household youth questionnaire
HZ Hypochromia
I1 Insulin (first venipuncture)
I2 Insulin (second venipuncture)
UI Iodine (urine)
FE Iron
SF Iron (from biochemistry profile)
LD Lactate dehydrogenase (from biochemistry profile)
L1 Latex antibody
LC LDL cholesterol (calculated)
PB Lead
LP Lipoprotein (a)
LH Luteinizing hormone
LU Lutein/zeaxanthin
LY Lycopene
LM Lymphocyte
MR Macrocyte
MC Mean cell hemoglobin (MCH)
MH Mean cell hemoglobin concentration (MCHC)
MV Mean cell volume (MCV)
PV Mean platelet volume
MA MEC adult questionnaire
MX MEC examination (general)
FF Dietary food frequency (ages 12-16 years)
MP MEC proxy questionnaire
MY MEC youth questionnaire
ME Metamyelocyte
MI Microcyte
MO Monocyte
MN Mononuclear cell
ML Myelocyte
CODE TOPIC
IC Normalized calcium (derived from ionized calcium)
OS Osmolality (from biochemistry profile)
PH Phlebotomy data collected in MEC (e.g., questions)
PS Phosphorus (from biochemistry profile)
PF Physical function evaluation
PE Physician's examination
PL Platelet
DW Platelet distribution width
PK Poikilocytosis
PO Polychromatophilia
SK Potassium (from biochemistry profile)
PR Promyelocyte
RC Red blood cell count (RBC)
RW Red cell distribution width (RDW)
RE Retinyl esters
RF Rheumatoid factor antibody
RU Rubella antibody
WT Sample weights
SE Selenium
SI Sickle cell
NA Sodium (from biochemistry profile)
SH Spherocyte
SP Spirometry
SD Survey design
TT Target cell
TE Tetanus
TB Total bilirubin (from biochemistry profile)
CA Total calcium
SC Total calcium (from biochemistry profile)
TC Total cholesterol
CH Total cholesterol (from biochemistry profile)
TI Total iron binding capacity (TIBC)
TP Total protein (from biochemistry profile)
TX Toxic granulation
TO Toxoplasmosis antibody
PX Transferrin saturation
TG Triglycerides
TR Triglycerides (from biochemistry profile)
TY Tympanometry
UA Uric acid (from biochemistry profile)
UB Urinary albumin
VU Vacuolated cells
VR Varicella antibody
VA Vitamin A
VB Vitamin B12
VC Vitamin C
VE Vitamin E
WC White blood cell count (WBC)
WW WISC/WRAT cognitive test
GENERAL REFERENCES
Delgado JL, Johnson CL, Roy I, Trevino FM. Hispanic Health and Nutrition
Examination Survey: methodological considerations. Amer J Pub Health
80(suppl.):6-10. 1990.
Engel A, Murphy RS, Maurer K, Collins E. Plan and operation of the HANES I
Augmentation Survey of Adults 25-74 Years, United States, 1974-75.
National Center for Health Statistics. Vital Health Stat 1(14). 1978.
Freeman DH, Freeman JL, Brock DB, Koch GG. Strategies in the multivariate
analysis of data from complex surveys II: an application to the United
States National Health Interview Survey. Int Stat Rev 40(3):317-30. 1976.
Khare M, Mohadjer LK, Ezzati-Rice TM, Waksberg J. An evaluation of
nonresponse bias in NHANES III (1988-91). 1994 Proceedings of the Survey
Research Methods section of the American Statistical Association. 1994.
Landis JR, Lepkowski JM, Eklund SA, Stehouwer SA. A statistical
methodology for analyzing data from a complex survey, the first National
Health and Nutrition Examination Survey. National Center for Health
Statistics. Vital Health Stat 2(92). 1982.
McDowell A, Engel A, Massey JT, Maurer K. Plan and operation of the second
National Health and Nutrition Examination Survey, 1976-80. National Center
for Health Statistics. Vital Health Stat 1(15). 1981.
Miller HW. Plan and operation of the Health and Nutrition Examination
Survey, United States, 1971-1973. National Center for Health Statistics.
Vital Health Stat 1(10a) and (10b). 1973.
National Center for Health Statistics. Plan and initial program of the
Health Examination Survey. Vital Health Stat 1(4). 1965.
National Center for Health Statistics. Plan and operation of a health
examination survey of U.S. youths 12-17 years of age. Vital Health Stat
1(8). 1969.
National Center for Health Statistics. Plan and operation of the Hispanic
Health and Nutrition Examination Survey, 1982-84. Vital Health Stat 1(19).
1985.
National Center for Health Statistics. Plan and operation of the Third
National Health and Nutrition Examination Survey, 1988-94. Vital Health
Stat 1(32). 1994.
National Center for Health Statistics. Plan, operation, and response
results of a program of children's examinations. Vital Health Stat 1(5).
1967.
Shah BV, Barnwell BG, Bieler GS. SUDAAN User's Manual: Software for
Analysis of Correlated Data. Research Triangle Park, NC: Research Triangle
Institute. Release 6.04. 1995.
Skinner CJ. Aggregated analysis: standard errors and significance tests.
In: Skinner CJ, Holt D, Smith TMF, eds. Analysis of complex surveys. New
York: John Wiley and Sons, Inc. 1989.
U.S. Department of Health and Human Services (DHHS). National Center for
Health Statistics. NHANES III reference manuals and reports (CD-ROM).
Hyattsville, MD: Centers for Disease Control and Prevention, 1996.
Available from National Technical Information Service (NTIS), Springfield,
VA. Acrobat .PDF format; includes access software: Adobe Systems, Inc.
Acrobat Reader 2.1.
Westat, Inc. A User's Guide to WesVarPC. Rockville, MD. Westat, Inc.
1996.
Yetley E, Johnson C. Nutritional applications of the Health and Nutrition
Examination Surveys (HANES). Annu Rev Nutr 7:441-63. 1987.
NHANES III LABORATORY DATA FILE
General Information
Introduction
The Laboratory Data File contains data from the urine collection and
venipuncture components of the examination, including almost all laboratory
test results (blood and urine) available to date. The exceptions are
discussed elsewhere in this documentation. In addition, auxiliary
information such as how long the examinee fasted, the time of day of the
venipuncture, and the conditions precluding venipuncture has been included.
This documentation presents information that should be reviewed before
proceeding with data analysis.
The documentation pertaining specifically to the Laboratory Data File is
divided into four main sections. The first section, "General Information,"
provides information about the contents of the Laboratory Data File. The
second section, "Data File Index," includes a brief description of all the
variables on the data set and shows the standard name of each variable and
its position in the data set. The third section, "Item Descriptions,
Codes, Counts, and Notes" provides for each component a description, the
standard variable name and a brief description of the values that variable
can take on, a count of the frequency of occurrence of each value, notes by
variable, and appendices as necessary. "References" are provided in the
fourth section.
Blood and urine specimens were collected on examinees aged one year and
older at the mobile examination center (MEC). For those examinees aged one
year and older who did not travel to the MEC, only blood specimens were
collected during the Home Examination (HE). Hematologic profiles were
completed for all examinees, and specified laboratory tests were performed
upon each specimen based on the examinee's age and sex. Only a limited
number of tests were performed on specimens collected during the Home
Examination. Appendix 1 lists the laboratory tests by specimen type, age
group, sex, and whether the specimen was collected in the Home Examination.
The analysis of NHANES III laboratory data must be conducted with the key
survey design and basic demographic variables. The NHANES III Household
Youth Questionnaire Data File (ages two months to 16 years) and the NHANES
III Household Adult Questionnaire Data File (ages 17 years and older)
contain demographic data, health indicators, and other related information
collected during household interviews. They also contain all survey design
variables and sample weights for these age groups. These two household
questionnaire files may be linked to the laboratory data file using the
unique survey participant (sample person) identifier SEQN.
Examinee Screening
Prior to the phlebotomy (venipuncture), a questionnaire was administered to
determine an examinee's eligibility for all phlebotomy procedures
(including venipuncture and the oral glucose tolerance test). It included
questions to determine if it was safe to perform the venipuncture, to
document and determine fasting compliance, and to aid in analyzing the
results of the laboratory tests performed. Examinees reporting hemophilia or
recent cancer chemotherapy treatment were excluded from the venipuncture.
For those examinees, the laboratory test results fields for all blood-based
laboratory tests were left blank. Because examinees reporting current
insulin therapy were excluded from receiving the oral glucose tolerance test
(OGTT), the plasma glucose (G2P), serum insulin (I2P) and serum C-peptide
(C2P) results from the second venipuncture were left blank as well.
Although examinees aged 12 years and older were instructed to fast for
10-16 hours prior to the morning examination or for six hours before the
afternoon or evening examination, the instructions were not followed
uniformly. Laboratory test results and the duration of the fast have been
included on the data file regardless of the examinee's fasting compliance.
Analysts should consider whether fasting status is crucial before undertaking
analyses. Examinees who reported insulin use during the household
interview were not instructed to fast.
Specimen Collection and Processing Procedures
Detailed specimen collection and processing instructions are discussed in
the Manual for Medical Technicians (U.S. DHHS, 1996). Vials were stored
under appropriate refrigerated (4-8 degrees Centigrade) or frozen (-20
degrees Centigrade) conditions until they were shipped to analytical
laboratories for testing. The analytical methods used by each of the
participating laboratories are described in the Laboratory Procedures Used
for NHANES III (U.S. DHHS, 1996). The manual contains quality control
graphs and statistical summary information for each laboratory test at the
end of the laboratory method description.
Oral glucose tolerance testing: During NHANES III, the OGTT was conducted
on MEC examinees aged 40-74 years. The protocol included two timed
venipunctures and a glucose drink. Two glucose drinks were used to measure
an examinee's ability to metabolize glucose -- Dextol(TM) and Trutol(TM).
After the first venipuncture, the examinee drank the glucose drink, and a
second venipuncture was performed approximately two hours later.
Examiner Training and Quality Control
The NHANES III laboratory staff consisted of medical technologists and
phlebotomists. The medical technologists held baccalaureates in medical
technology. Both they and the phlebotomists were certified by the American
Society for Clinical Pathologists or by a similar organization.
All laboratory staff completed comprehensive training in standardized
laboratory procedures before they began working in the MEC. The MEC
phlebotomists completed comprehensive training in pediatric phlebotomy
techniques, including instruction by a pediatric nurse practitioner.
Laboratory team performance was monitored using several techniques. NCHS
and contract consultants used a structured quality assurance evaluation
during unscheduled visits to evaluate both the quality of the laboratory work
and the quality-control procedures. Each laboratory staff person was
observed for equipment operation, specimen collection and preparation, and
testing procedures, and constructive feedback was given to each team. Formal
retraining sessions were conducted annually to ensure that required skill
levels were maintained.
Laboratory Protocol Changes from 1988 to 1994
Most laboratory tests were performed for the entire six years of NHANES
III. Exceptions are detailed below. Apolipoprotein AI and B tests were
included during 1988-1991 only. Lipoprotein(a), Vitamin B12, and antibody
tests for immunoglobulin E, rubella, varicella, and toxoplasmosis were
conducted during 1991-1994. For the 1991-1994 period, the OGTT procedure was
modified to add tests for C-peptide and insulin on specimens from the second
venipuncture. For statistical analyses of these laboratory test results, the
appropriate Phase 1 or Phase 2 sample weight should be used.
Incomplete Data Release
At the time of this data release, some laboratory test results were not
available. Tests for which results were unavailable included vitamin D,
immunoglobulin E, diphtheria antitoxin, measles antibody, homocysteine,
periodontal pathogens, thyroxine, thyroid stimulating hormone,
antithyroglobulin antibody, antimicrosomal antibody, and methylmalonic
acid. Cotinine test results for 1988-1991 have been included in this
laboratory data file. Cotinine testing is still being carried out for
1991-1994, and the laboratory test results will be released at a future date.
Results from urine pregnancy tests are included in the NHANES III Examination
Data File, rather than in the Laboratory Data File.
Serologic testing for human immunodeficiency virus (HIV) antibody and urine
testing for drugs of abuse were performed anonymously. The drugs of abuse
for which examinees were tested were cocaine, marijuana, opiates,
phencyclidine, and amphetamines. To maintain anonymity, the examinee's
serum and urine were labeled with a random identifying number, and limited
demographic data were linked to that number. The new identifier was not
linked to the original sample identifier. Therefore, these data cannot be
linked to other NHANES III data. The HIV test was performed from 1988
through 1994; the urine drug testing was done from 1991 through 1994.
Because of the limited analytic potential of the HIV and drug data, this
file is not included in this data release.
Data Preparation and Processing
For laboratory tests with a lower detection limit, results below the lower
detection limit were replaced with a value equal to the detection limit
divided by the square root of two. This value was created to help the user
distinguish a nondetectable laboratory test result from a measured
laboratory test result. Appendix 2 documents the detection limit for each
laboratory test.
The SI unit (le Systeme International d Unites) is an outgrowth of the
metric system that has been used throughout most of the world. In addition
to providing a uniform international system of units of measurement, a
uniform style is prescribed. Laboratory test results not originally reported
in SI units were converted to SI units if applicable. Conversion factors,
the format of the NHANES and SI results, and NHANES and SI units of measure
are in Appendix 3. In converting NHANES III data to SI units, the goal was
to preserve the level of detail reported by the laboratories in the original
laboratory test result. Therefore, the number of significant digits in the
laboratory test results data may be different from that in published
references.
The Laboratory Data File contains laboratory test results for glucose
(G1P), triglycerides (TGP), cholesterol (TCP), and iron (FEP) measured by
contract laboratories using reference analytic methods. For these methods,
consult the Laboratory Procedures Used for NHANES III (U.S. DHHS, 1996).
However, the biochemistry profile also included measurements of these
analytes. In general, for most analyses, the appropriate variables to use
are G1P, TGP, TCP and FEP. The values from the biochemistry profile (SGP,
CHP, TRP, SFP) should not be used routinely.
The definition of a reference method by the National Committee for Clinical
Laboratory Standards (NCCLS) is "a thoroughly investigated method in which
exact and clear descriptions of the necessary conditions and procedures are
given for the accurate determination of one or more property values; the
documented accuracy and precision of the method are commensurate with the
method's use for assessing the accuracy of other methods for measuring the
same property values or for assigning reference method values to reference
materials" (NCCLS, 1991).
NHANES III Laboratory Data File Index
Whole Blood, Serum, Plasma, and Urine Data
------------------------------------------------------------------------
Variable
Description Name Positions
------------------------------------------------------------------------
DEMOGRAPHIC DATA
HOUSEHOLD SCREENER QUESTIONNAIRE (HSQ)
Sample person identification number ......... SEQN 1-5
Family sequence number ...................... DMPFSEQ 6-10
Examination/interview Status ................ DMPSTAT 11
Race-ethnicity .............................. DMARETHN 12
Race ........................................ DMARACER 13
Ethnicity ................................... DMAETHNR 14
Sex ......................................... HSSEX 15
Age at interview (Screener) ................. HSAGEIR 16-17
Age at interview - unit (Screener) .......... HSAGEU 18
Age in months at interview (screener) ....... HSAITMOR 19-22
Family size (persons in family) ............. HSFSIZER 23-24
Household size (persons in dwelling) ........ HSHSIZER 25-26
County code ................................. DMPCNTYR 27-29
FIPS code for State ......................... DMPFIPSR 30-31
Rural/urban code based on USDA code ......... DMPMETRO 32
Census region, weighting(Texas in south) .... DMPCREGN 33
Poverty Income Ratio (unimputed income) ..... DMPPIR 34-39
SURVEY DESIGN DATA
Phase of NHANES III survey .................. SDPPHASE 40
NHANES III Laboratory Data File Index
Whole Blood, Serum, Plasma, and Urine Data
------------------------------------------------------------------------
Variable
Description Name Positions
------------------------------------------------------------------------
Total NHANES III pseudo-PSU ................. SDPPSU6 41
Total NHANES III pseudo-stratum ............. SDPSTRA6 42-43
Pseudo-PSU for phase 1 ...................... SDPPSU1 44
Pseudo-stratum for phase 1 .................. SDPSTRA1 45-46
Pseudo-PSU for phase 2 ...................... SDPPSU2 47
Pseudo-stratum for phase 2 .................. SDPSTRA2 48-49
SAMPLING WEIGHTS - TOTAL NHANES III (1988-94)
Total interviewed sample final weight ....... WTPFQX6 50-58
Total MEC-examined sample final weight ...... WTPFEX6 59-67
Total M+H examined sample final weight ...... WTPFHX6 68-76
Total allergy subsample final weight ........ WTPFALG6 77-85
Total CNS subsample final weight ............ WTPFCNS6 86-94
Total morning subsample final wgt ........... WTPFSD6 95-103
Total afternoon/eve subsample final wgt ..... WTPFMD6 104-112
Total M+H morning subsample final wgt ....... WTPFHSD6 113-121
Total M+H afternoon subsample final wgt ..... WTPFHMD6 122-130
SAMPLING WEIGHTS - NHANES III PHASE 1 (1988-91)
Phase 1 interviewed sample final wgt ........ WTPFQX1 131-139
Phase 1 MEC examined sample final wgt ....... WTPFEX1 140-148
Phase 1 M+H examined sample final wgt ....... WTPFHX1 149-157
Phase 1 allergy subsample final wgt ......... WTPFALG1 158-166
Phase 1 CNS subsample final wgt ............. WTPFCNS1 167-175
Phase 1 morning sess subsample final wgt .... WTPFSD1 176-184
Phase 1 aft/eve subsample final wgt ......... WTPFMD1 185-193
Phase 1 morning M+H subsample final wgt ..... WTPFHSD1 194-202
Phase 1 aft/eve M+H subsample final wgt ..... WTPFHMD1 203-211
SAMPLING WEIGHTS - NHANES III PHASE 2 (1991-94)
Phase 2 interviewed sample final wgt ........ WTPFQX2 212-220
Phase 2 MEC examined sample final wgt ....... WTPFEX2 221-229
NHANES III Laboratory Data File Index
Whole Blood, Serum, Plasma, and Urine Data
------------------------------------------------------------------------
Variable
Description Name Positions
------------------------------------------------------------------------
Phase 2 M+H examined sample final wgt ....... WTPFHX2 230-238
Phase 2 allergy subsample final wgt ......... WTPFALG2 239-247
Phase 2 CNS subsample final wgt ............. WTPFCNS2 248-256
Phase 2 morning sess subsample final wgt .... WTPFSD2 257-265
Phase 2 aft/eve subsample final wgt ......... WTPFMD2 266-274
Phase 2 morning M+H subsample final wgt ..... WTPFHSD2 275-283
Phase 2 aft/eve M+H subsample final wgt ..... WTPFHMD2 284-292
FAY'S BRR REPLICATE INTERVIEW WEIGHTS - TOTAL NHANES III (1988-94)
Replicate 1 final interview weight .......... WTPQRP1 293-301
Replicate 2 final interview weight .......... WTPQRP2 302-310
Replicate 3 final interview weight .......... WTPQRP3 311-319
Replicate 4 final interview weight .......... WTPQRP4 320-328
Replicate 5 final interview weight .......... WTPQRP5 329-337
Replicate 6 final interview weight .......... WTPQRP6 338-346
Replicate 7 final interview weight .......... WTPQRP7 347-355
Replicate 8 final interview weight .......... WTPQRP8 356-364
Replicate 9 final interview weight .......... WTPQRP9 365-373
Replicate 10 final interview weight ......... WTPQRP10 374-382
Replicate 11 final interview weight ......... WTPQRP11 383-391
Replicate 12 final interview weight ......... WTPQRP12 392-400
Replicate 13 final interview weight ......... WTPQRP13 401-409
Replicate 14 final interview weight ......... WTPQRP14 410-418
Replicate 15 final interview weight ......... WTPQRP15 419-427
Replicate 16 final interview weight ......... WTPQRP16 428-436
Replicate 17 final interview weight ......... WTPQRP17 437-445
Replicate 18 final interview weight ......... WTPQRP18 446-454
Replicate 19 final interview weight ......... WTPQRP19 455-463
Replicate 20 final interview weight ......... WTPQRP20 464-472
Replicate 21 final interview weight ......... WTPQRP21 473-481
Replicate 22 final interview weight ......... WTPQRP22 482-490
Replicate 23 final interview weight ......... WTPQRP23 491-499
Replicate 24 final interview weight ......... WTPQRP24 500-508
Replicate 25 final interview weight ......... WTPQRP25 509-517
Replicate 26 final interview weight ......... WTPQRP26 518-526
Replicate 27 final interview weight ......... WTPQRP27 527-535
NHANES III Laboratory Data File Index
Whole Blood, Serum, Plasma, and Urine Data
------------------------------------------------------------------------
Variable
Description Name Positions
------------------------------------------------------------------------
Replicate 28 final interview weight ......... WTPQRP28 536-544
Replicate 29 final interview weight ......... WTPQRP29 545-553
Replicate 30 final interview weight ......... WTPQRP30 554-562
Replicate 31 final interview weight ......... WTPQRP31 563-571
Replicate 32 final interview weight ......... WTPQRP32 572-580
Replicate 33 final interview weight ......... WTPQRP33 581-589
Replicate 34 final interview weight ......... WTPQRP34 590-598
Replicate 35 final interview weight ......... WTPQRP35 599-607
Replicate 36 final interview weight ......... WTPQRP36 608-616
Replicate 37 final interview weight ......... WTPQRP37 617-625
Replicate 38 final interview weight ......... WTPQRP38 626-634
Replicate 39 final interview weight ......... WTPQRP39 635-643
Replicate 40 final interview weight ......... WTPQRP40 644-652
Replicate 41 final interview weight ......... WTPQRP41 653-661
Replicate 42 final interview weight ......... WTPQRP42 662-670
Replicate 43 final interview weight ......... WTPQRP43 671-679
Replicate 44 final interview weight ......... WTPQRP44 680-688
Replicate 45 final interview weight ......... WTPQRP45 689-697
Replicate 46 final interview weight ......... WTPQRP46 698-706
Replicate 47 final interview weight ......... WTPQRP47 707-715
Replicate 48 final interview weight ......... WTPQRP48 716-724
Replicate 49 final interview weight ......... WTPQRP49 725-733
Replicate 50 final interview weight ......... WTPQRP50 734-742
Replicate 51 final interview weight ......... WTPQRP51 743-751
Replicate 52 final interview weight ......... WTPQRP52 752-760
FAY'S BRR REPLICATE EXAMINATION WEIGHTS - TOTAL NHANES III (1988-94)
Replicate 1 final exam weight ............... WTPXRP1 761-769
Replicate 2 final exam weight ............... WTPXRP2 770-778
Replicate 3 final exam weight ............... WTPXRP3 779-787
Replicate 4 final exam weight ............... WTPXRP4 788-796
Replicate 5 final exam weight ............... WTPXRP5 797-805
Replicate 6 final exam weight ............... WTPXRP6 806-814
Replicate 7 final exam weight ............... WTPXRP7 815-823
Replicate 8 final exam weight ............... WTPXRP8 824-832
Replicate 9 final exam weight ............... WTPXRP9 833-841
NHANES III Laboratory Data File Index
Whole Blood, Serum, Plasma, and Urine Data
------------------------------------------------------------------------
Variable
Description Name Positions
------------------------------------------------------------------------
Replicate 10 final exam weight .............. WTPXRP10 842-850
Replicate 11 final exam weight .............. WTPXRP11 851-859
Replicate 12 final exam weight .............. WTPXRP12 860-868
Replicate 13 final exam weight .............. WTPXRP13 869-877
Replicate 14 final exam weight .............. WTPXRP14 878-886
Replicate 15 final exam weight .............. WTPXRP15 887-895
Replicate 16 final exam weight .............. WTPXRP16 896-904
Replicate 17 final exam weight .............. WTPXRP17 905-913
Replicate 18 final exam weight .............. WTPXRP18 914-922
Replicate 19 final exam weight .............. WTPXRP19 923-931
Replicate 20 final exam weight .............. WTPXRP20 932-940
Replicate 21 final exam weight .............. WTPXRP21 941-949
Replicate 22 final exam weight .............. WTPXRP22 950-958
Replicate 23 final exam weight .............. WTPXRP23 959-967
Replicate 24 final exam weight .............. WTPXRP24 968-976
Replicate 25 final exam weight .............. WTPXRP25 977-985
Replicate 26 final exam weight .............. WTPXRP26 986-994
Replicate 27 final exam weight .............. WTPXRP27 995-1003
Replicate 28 final exam weight .............. WTPXRP28 1004-1012
Replicate 29 final exam weight .............. WTPXRP29 1013-1021
Replicate 30 final exam weight .............. WTPXRP30 1022-1030
Replicate 31 final exam weight .............. WTPXRP31 1031-1039
Replicate 32 final exam weight .............. WTPXRP32 1040-1048
Replicate 33 final exam weight .............. WTPXRP33 1049-1057
Replicate 34 final exam weight .............. WTPXRP34