Table of Contents

Component Description

Overweight and obesity is a major public health problem among children and adolescents in the United States. Regular physical activity promotes health and fitness and may help to prevent obesity. As the part of the NHANES National Youth Fitness Survey (NNYFS) specific data collection effort, the body measures data are used to study the associations between body weight and measures of physical activity and fitness, and to estimate the prevalence of overweight and obesity in U.S. children and adolescents.

Eligible Sample

All survey participants aged 3 to 15 years were eligible for the body measures component.

Protocol and Procedure

The NNYFS body measures data were collected in the Mobile Examination Center (MEC) by trained health technicians. Generally, one technician completed the measurements and data recording. Occasionally, one technician conducted the measurements and another technician assisted in data recording. Standing height was measured using a portal stadiometer. Weight was measured using a portal digital weight scale. Arm length and arm, waist, and calf circumferences were measured using a steel measuring tape. Calf, triceps, and subscapular skinfolds were measured using a skinfold caliper. Arm and calf measurements were made on the right side of the body. If a participant had a medical condition or medical appliance, such as a cast, that prevented measurements from being taken on the right side of the body, the health technician took measurements on the left side. All measurements were entered into the NNYFS database by the health technician.

Please refer to the NNYFS Body Measures Procedures Manual (https://www.cdc.gov/nchs/nnyfs/manuals.htm) for further details on obtaining body measures.

Quality Assurance & Quality Control

The NNYFS health technicians completed at least 12 hours of training with survey staff and an expert anthropometrist. The training included an overview of the component, using the NHANES III anthropometry video, and demonstrations conducted by the expert examiner with volunteer subjects. The expert examiner reviewed and demonstrated the proper technique to use for each measurement. Supervised practice exercises followed, conducted with several volunteer subjects aged 3 to 15 years. Health technician performance was monitored using direct observation, data reviews, and periodic expert examiner (gold standard comparison) evaluations.

The body measures examination areas in each of the MECs were identical with respect to layout and equipment. Scheduled equipment calibration was performed by the health technicians. The NNYFS Body Measures Procedures Manual includes detailed descriptions of the quality assurance and quality control measures that are used in the NNYFS body measures component.

Data Processing and Editing

The NNYFS body measures data were reviewed for unusual and erroneous values. Review criteria were based on NHANES 1999–2010 body measures data for children ages of 3 to 15 years. During the data review, values that were above the 99th percentile or below the 1st percentile, for a particular age or age-gender group, were flagged for review. When records were flagged, the entire body measures record was reviewed for reasonableness. Subject characteristics such as height, weight, age and gender were taken into consideration. Values that were determined to be unrealistic were deleted from the file. None of the original body measures data were changed and there are no imputed values in this file.

Body Mass Index (BMXBMI):
Body Mass Index (BMI) was calculated as weight in kilograms divided by height in meters squared, and then rounded to one decimal place.

BMI Category – Children/Adolescents (BMDBMIC):
This variable was created for all participants aged 3 to 15 years. Cutoff criteria are based on the Centers for Disease Control and Prevention's sex-specific 2000 BMI-for-age growth charts for the United States. Age in months at examination was used to match age in months from BMI growth chart data, separately for males and females. There are four codes:

  1. Underweight (BMI < 5th percentile)
  2. Normal weight (BMI 5th to < 85th percentile)
  3. Overweight (BMI 85th to < 95th percentile)
  4. Obese (BMI ≥ 95th percentile)

 

Analytic Notes

Component status code: A final body measures component status code (BMDSTATS) provides analysts with a quick method of identifying survey participants with complete or partial body measurement data.

Unusual values: Unusual body measures values were noted during the review of the data. Typically, unusual values occurred when a subject was extremely short, tall, overweight or underweight. Analysts should examine the distributions of the body measurements carefully and consider whether or not it is appropriate to include or exclude extreme values in a given analysis.

Comment codes: Comment codes were added by the health technicians, during data collection, to document problems or situations that arose during the body measures examination. For example, the variable BMIWT is a comment code for the body weight measurement. If a participant did not wear light shorts and t-shirt or did not change into the NNYFS lightclothing, a code of BMIWT of “3” denoting “regular clothing worn” was made in the record. Analysts should review the comment code information for each of the body measures prior to data analysis.

Weight status classification: BMI, expressed as weight in kilograms divided by height in meters squared (kg/m2), is commonly used to classify weight status. The age-and sex-specific 5th, 85th, and 95th percentiles of the 2000 CDC growth charts are usually used as cutoff criteria for children and adolescents. The variable BMDBMIC provides weight status categories for participants aged 3 to 15 years at examination. Information about age in years at screening (RIDAGEYR) and at examination (RIDEXAGY) is available in the NNYFS Demographic data file.

The analysis of NNYFS body measures data must be conducted using the appropriate survey design variables, sample weights, and the basic demographic variables. Please refer to the NNYFS Analytic Guidelines for details on the use of sample weights and other analytic issues.

References

Codebook and Frequencies

SEQN - Respondent sequence number

Variable Name:
SEQN
SAS Label:
Respondent sequence number
English Text:
Respondent sequence number.
Target:
Both males and females 3 YEARS - 15 YEARS

BMDSTATS - Body Measures Component Status Code

Variable Name:
BMDSTATS
SAS Label:
Body Measures Component Status Code
English Text:
Body Measures Component status Code
Target:
Both males and females 3 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Complete 1416 1416
2 Partial: Only height and weight obtained 3 1419
3 Other partial exam 154 1573
4 No body measures exam data 3 1576
. Missing 0 1576

BMXWT - Weight (kg)

Variable Name:
BMXWT
SAS Label:
Weight (kg)
English Text:
Weight (kg)
Target:
Both males and females 3 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
12.3 to 136.9 Range of Values 1571 1571
. Missing 5 1576

BMIWT - Weight Comment

Variable Name:
BMIWT
SAS Label:
Weight Comment
English Text:
Weight Comment
Target:
Both males and females 3 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Could not obtain 2 2
2 Exceeds capacity 0 2
3 Clothing 18 20
4 Medical appliance and/or shoes 2 22
. Missing 1554 1576

BMXHT - Standing Height (cm)

Variable Name:
BMXHT
SAS Label:
Standing Height (cm)
English Text:
Standing Height (cm)
Target:
Both males and females 3 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
89.7 to 188.9 Range of Values 1571 1571
. Missing 5 1576

BMIHT - Standing Height Comment

Variable Name:
BMIHT
SAS Label:
Standing Height Comment
English Text:
Standing Height Comment
Target:
Both males and females 3 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Could not obtain 2 2
2 Exceeds capacity 0 2
3 Not straight 0 2
. Missing 1574 1576

BMXBMI - Body Mass Index (kg/m**2)

Variable Name:
BMXBMI
SAS Label:
Body Mass Index (kg/m**2)
English Text:
Body Mass Index (kg/m**2)
Target:
Both males and females 3 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
11.9 to 48.3 Range of Values 1571 1571
. Missing 5 1576

BMDBMIC - BMI Category - Children/Adolescents

Variable Name:
BMDBMIC
SAS Label:
BMI Category - Children/Adolescents
English Text:
BMI Category - Children/Adolescents
Target:
Both males and females 3 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Underweight 42 42
2 Normal weight 959 1001
3 Overweight 266 1267
4 Obese 304 1571
. Missing 5 1576

BMXARML - Upper Arm Length (cm)

Variable Name:
BMXARML
SAS Label:
Upper Arm Length (cm)
English Text:
Upper Arm Length (cm)
Target:
Both males and females 3 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
17.3 to 42.5 Range of Values 1568 1568
. Missing 8 1576

BMIARML - Upper Arm Length Comment

Variable Name:
BMIARML
SAS Label:
Upper Arm Length Comment
English Text:
Upper Arm Length Comment
Target:
Both males and females 3 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Could not obtain 0 0
. Missing 1576 1576

BMXARMC - Arm Circumference (cm)

Variable Name:
BMXARMC
SAS Label:
Arm Circumference (cm)
English Text:
Arm Circumference (cm)
Target:
Both males and females 3 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
13.7 to 46.8 Range of Values 1569 1569
. Missing 7 1576

BMIARMC - Arm Circumference Comment

Variable Name:
BMIARMC
SAS Label:
Arm Circumference Comment
English Text:
Arm Circumference Comment
Target:
Both males and females 3 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Could not obtain 1 1
. Missing 1575 1576

BMXWAIST - Waist Circumference (cm)

Variable Name:
BMXWAIST
SAS Label:
Waist Circumference (cm)
English Text:
Waist Circumference (cm)
Target:
Both males and females 3 YEARS - 15 YEARS
Hard Edits:
0.0000 to 200.0000
Code or Value Value Description Count Cumulative Skip to Item
42.5 to 144.7 Range of Values 1568 1568
. Missing 8 1576

BMIWAIST - Waist Circumference Comment

Variable Name:
BMIWAIST
SAS Label:
Waist Circumference Comment
English Text:
Waist Circumference Comment
Target:
Both males and females 3 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Could not obtain 1 1
. Missing 1575 1576

BMXCALF - Maximal Calf Circumference (cm)

Variable Name:
BMXCALF
SAS Label:
Maximal Calf Circumference (cm)
English Text:
Maximal Calf Circumference (cm)
Target:
Both males and females 3 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
18.3 to 55.9 Range of Values 1566 1566
. Missing 10 1576

BMICALF - Maximal Calf Comment

Variable Name:
BMICALF
SAS Label:
Maximal Calf Comment
English Text:
Maximal Calf Comment
Target:
Both males and females 3 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Could not obtain 2 2
. Missing 1574 1576

BMXCALFF - Calf Skinfold (mm)

Variable Name:
BMXCALFF
SAS Label:
Calf Skinfold (mm)
English Text:
Calf Skinfold (mm)
Target:
Both males and females 3 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
3.7 to 39.9 Range of Values 1442 1442
. Missing 134 1576

BMICALFF - Calf Skinfold Comment

Variable Name:
BMICALFF
SAS Label:
Calf Skinfold Comment
English Text:
Calf Skinfold Comment
Target:
Both males and females 3 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Could not obtain 122 122
2 Exceeds capacity 3 125
. Missing 1451 1576

BMXTRI - Triceps Skinfold (mm)

Variable Name:
BMXTRI
SAS Label:
Triceps Skinfold (mm)
English Text:
Triceps Skinfold (mm)
Target:
Both males and females 3 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
4 to 38.8 Range of Values 1553 1553
. Missing 23 1576

BMITRI - Triceps Skinfold Comment

Variable Name:
BMITRI
SAS Label:
Triceps Skinfold Comment
English Text:
Triceps Skinfold Comment
Target:
Both males and females 3 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Could not obtain 15 15
2 Exceeds capacity 0 15
. Missing 1561 1576

BMXSUB - Subscapular Skinfold (mm)

Variable Name:
BMXSUB
SAS Label:
Subscapular Skinfold (mm)
English Text:
Subscapular Skinfold (mm)
Target:
Both males and females 3 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
3.7 to 38 Range of Values 1507 1507
. Missing 69 1576

BMISUB - Subscapular Skinfold Comment

Variable Name:
BMISUB
SAS Label:
Subscapular Skinfold Comment
English Text:
Subscapular Skinfold Comment
Target:
Both males and females 3 YEARS - 15 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Could not obtain 59 59
2 Exceeds capacity 4 63
. Missing 1513 1576