The NHANES obtains measured weights in examination gowns and heights without shoes. BMI is calculated by dividing weight in kilograms by the square of height in meters.
In 1997, a Consultation on Obesity convened by the World Health Organization recommended standardizing the classification of overweight and obesity. Obesity was defined as a BMI of 30.0 or greater. Further classification of obesity was made as follows: 30.0-34.9 was defined as Class I obesity, 35.0-39.9 as Class II, and 40.0 or greater as Class III. The Expert Panel on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults, convened by NIH in 1998 adopted general concepts of the World Health Organization classification system and it has now been endorsed by more than 50 professional medical societies, consumer groups, and government agencies. For this objective, therefore, a BMI cut point of 30.0 was chosen for adults aged 20 years and older.
Pregnant women are excluded from the numerator and denominator.