Key Concepts About NHANES I Data Structure

Conduct of Study

NHANES I was conducted from 1971-1975.  Population subgroups considered to be at high risk of malnutrition were oversampled.  Approximately 32,000 persons ages 1-74 years old were interviewed and 23,808 received a medical examination.  The majority of survey components were completed by June of 1974. 

However, a subsample of 3,854 individuals was selected to receive a detailed medical examination component.  The detailed medical examination component was extended past the June 1974 date until October 1975, in order to reach a total detailed sample of just over 6,900 persons. The detailed subsample represents the civilian, non-institutionalized population of the United States aged 25-74 years at the midpoint of the survey, without any oversampling. Other specialized subsamples are also available for analyses, however most analysts will require either major components utilizing data from the main sample taken from stands 1-65, or the detailed medical examination data from all stands 1-100, or both.  The other subsample categories are rarely used. 

 

Data File Releases

NHANES I data were originally released in a series of separate data tapes, and are currently available as ASCII files on the NHANES website.  All the data tapes contained demographic information such as age, gender, race, income, occupation and education. The household adult file contains survey design variables, such as weights, strata and primary sampling units, and demographic variables. In addition,  it contains data collected through the household adult questionnaire administered to survey participants aged 17 years and older during the household interview.  Each tape thereafter focused on a particular component of the survey, according to the method of data collection.

 The categories listed below represent data collected from the general survey and medical examination.

For the detailed medical examination subsample, in addition to the information collected above, the following data file releases are also available (along with additional laboratory determinations).

info iconIMPORTANT NOTE

Typically, most analysts will extract data from several of these data files and merge them into one data file to do their analyses.  All analysts should be aware that the demographic information, while standard to each tape, is only provided for the actual persons who participated in that component.  This means that when you choose to merge different tapes, you should be careful to extract your demographic variables from the tape with the largest number of records.

 

Data Files

Several of the data files are very large, and variables tend to be grouped as they were in the questionnaires.  Care should be taken to search multiple data files, as some items of interest, such as aspirin use, were ascertained on both the general population and the detailed subsample (e.g. biochemistry and arthritis data files).   For more information on how to search NHANES I data file documentation, please see the Locate Variables module.

In the animated explanation, linked below, click the headings to see examples of the types of data to be found in some of the various data files constituting the NHANES I data releases. Or, review the table below see examples of the types of data to be found in some of the various data files constituting the NHANES I data releases.

 

View an animated explanation of the component descriptions.

NHANES I - Data Files and Variables
File No. Abbr Title Sample Size Stands Contents Comments
4111

BM

Anthropometry Goniometry, Skeletal Age, Bone Density,
and Cortical Thickness,
Ages 1-74 years

23,808

1-35

1-65  

1-100

Height and weight, body and skin-fold measurements for all examinees.  Some data imputed.

Some data collected only on detailed examinees. X-rays of the hand and wrist were taken of examinees 1-17 years of age.

Goniometry data was collected for detailed examinees aged 25-74 years only at stands 1-35.

4800

LB

Biochemistry, Serology, Hematology, Blood
Slides, Urine Dipst.

23,808

1-65

1-100

66-100

Measurements of blood and urine samples.  Some data imputed.

Some data collected only on detailed examinees.  For stands 66-100 collected urobilinogen, bilirubin, ketones; and serum sodium, potassium, folate; and syphilis.

4233

ME

Medical Examination,
Ages 1-74 years

23,808

1-65

1-100 66-100

Physician examination findings focused on the clinical signs of nutritional deficiencies plus other abnormal findings.

Those in the detailed sample were examined more thoroughly with additional emphasis given to the cardiovascular, respiratory, and musculoskeletal systems, and the ears, nose and throat. For stands 66-100 the physician also examined occular fundi.

4235

OH

Dental,
Ages 1-74 years

20,749

1-65

Dental examination findings

None

4151

DE

Dermatology,
Ages 1-74 years

20,749

1-65

Complete clinical examination of the skin and subcutaneous tissue.

None

4701

FF

Dietary Frequency
and Adequacy,
Ages 1-74 years

20,749

1-65

The first half consists of food frequency data. The second summarizes the total nutrient intake from the 24-hour recall record by selected nutrients and evaluates that nutrient intake in relation to selected dietary intake standards used in NHANES I.

None

4704

DR

24-Hour Food
Consumption Intake,
Ages 1-74 years

20,749

1-65

The 20,749 respondents were asked to report each food they had consumed the day before the exam (midnight to midnight). It included foods eaten on Monday through Friday, but generally excluded foods eaten on weekends.

The total number of records found on the file is 371,889. However, there are only 20,749 different examined persons, each with 50 possible data records, one for each food item consumed.

 

4081

AH

Medical History
Questionnaire,
Ages 12-74 years

18,836

1-65

1-100

66-100

A detailed medical history administered by an interviewer.

Two questions on bone fractures were asked only in stands 66-100.  Some questions asked only in stands 1-65.

4067

CH

Medical History
Questionnaire,
Ages 1-11 years

4,972

1-65

A medical history administered by an interviewer and asked of the parents of the child.

Parts of the questionnaire were asked for children ages 1-5 years and other parts were asked for those ages 6-11 years.

4121

AR

Arthritis Data

6,913

1-65

1-100

Detailed arthritis questions only given to those who responded positively to the initial screening questions in the medical exam.

The examining physician could skip the arthritis supplement if he re-questioned the survey participant and thought the screening questions should be changed to negative.  However, sometimes the physician failed to recode the responses.  Also, all men had x-rays of the hips, but only women aged 50 years and older were given hip x-rays.

4241

AU

Audiometric

6,913

1-65

1-100 66-100

Audiometric tests--air-conduction, bone-conduction and speech reception.

Air-conduction testing levels were obtained for all examinees in stands 1-65.  Bone-conduction hearing thresholds were obtained for detailed examinees in stands 1-65. The speech component was administered to those in stands 66-100.

4251

XR

Chest X-Ray, Pulmonary Diffusion, and Tuberculin
Test Results,
Ages 25-74 years

6,913

1-65

1-100 66-100

As described in the title, plus detailed notes on lung and heart size measurement techniques, cardiopulmonary pathology assessment criteria, and adjudication procedures.

One typewritten (not handwritten like the other files) asterisk denotes data from stands 1-65, and two asterisks denote data from stands 66-100.

4140

EK

Computer Measurements
and Interpretations of Electrocardiograms, 
Ages 25-74 years

6,913

1-100

Single channel data, 2.5 seconds per lead and sampled at 500 samples per second. 

ECG data quality is in general poor. This automated ECG program (ECAN-E, U.S. Public Health Service) from these single channel data did not produce stable ECG wave measurements.

*

EC

Electrocardiogram

6,316

1-100

Single channel data, 2.5 seconds per lead and sampled at 500 samples per second. 

This dataset attempts to correct for the problem of the earlier ECG dataset.  Some improvement was gained.  READ DOCUMENTATION!  Although the documentation states this file includes three data files - one each from NHANES I, II, and III - it does not.  Each file is located on its respective survey website.  However, all data files name their variables the same as NHANES III. 

4171

MH

General Well-Being and the
CES-D Depression Scale Developed by The National Institute of Mental Health,
Ages 25-74 years

6,913

1-65

1-100 66-100

The only explicitly psychological component of NHANES I. The response options for the major data elements have been recoded from the form used to obtain initial responses to ordinal values such that a higher  numerical score reflects a higher representation of psychological well-being.

The 20 questions in the fourth section were administered for stands 66-100. The distribution of the responses to the four positive questions (Positions 282, 286, 290, 294) differed substantially from the pattern formed by the responses to the negative questions.

Cross-tabulation of the responses to each of the 4 questions with a sub-scale formed from the 16 negative items revealed inconsistencies great enough to caution the user against an uncritical use of these items, either singularly or in scales.

4091

GM

Health Care Needs, General Medical History Supplement, and Respiratory and Cardiovascular Supplements,
Ages 25-74 years

6,913

1-65

1-100 66-100

Additional health histories on the persons in the detailed examination sample.

The General Medical History was given by the Health Examination Representative for stands 1-65 and by the Census interviewer for stands 66-100. The Sample Person Supplement contained questions removed from the Medical History, the General Medical History and some additional questions not asked in the first 65 locations.

4250

SP

Spirometry-Best Trials Only, Ages 25-74 years

6,913

1-65

1-100

Forced Expiratory Spirogram results from 5 maximal expirations. Significant data clean-up plus a provisional diagnosis based on the FEV/FVC ratio and the relationship between predicted and observed FVCs. A diagnosis of normal, restrictive, obstructive or restrictive/obstructive was appended. The output from this step consisted of 5,544 trials.

Some respondents could not perform an acceptable FES while others had comprehension or discomfort problems.  Minimal imputation.

4163

VI

Near and Distant Vision,
Ages 25-74 years

3,059

66-100

Distance vision measures using illuminated wall charts from a distance of 20 ft.  Near vision test at “smallest read satisfactorily” for respondent.

Only stands 66-100.

4161

OP

Ophthalmology,
Ages 1-74 years

10,127

1-35

Eye examination for ages 1-74 which included the taking of an ocular history regarding previously known eye disorders or previous eye surgery and an examination for motility defects.

Only stands 1-35. For ages 3 years and over included a determination of monocular distance visual acuity with usual correction, and a pinhole test to determine correctability for those with acuity less than 20/20. Also includes spherical trial lens test for examinees with acuity less than 20/40, and applanation tonometry on examinees 20 years and older. For detailed examinees ages 25-74 it included prescription of present glasses; dilation, within 20-70 minutes following dilation retinoscopy with acuity less than 20/40.

4702

MG

Model Gram

n/a

1-65

The Model Gram File consists of food items in numeric order with designated food group numbers, food codes, alphanumeric descriptions, preferred model codes and their gram conversion factors.

This file is the basis for coding all reported food items for the 24-Hour Recall Intake File.

4703

NC

Nutrient Composition

n/a

1-65

The Nutrient Composition Data Bank File is the actual nutrient analysis in 100 gram edible portions of all codes listed in the Model Gram File.

This file is also essential for recording and analyzing the actual 24-Hour Recall Intake File.

* These data were released many years later on CD-ROM, never on data tape. Therefore, there is no tape number.

 

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