Validity of anthropometry in classifying youths as obese

Using densitometrically-determined percentage body fat as the criterion of true obesity, 316 youths aged 8.4-18.99 years were classified as obese or not obese using conventional referent values for five anthropometric indicators of obesity (weight, BMI, triceps skinfold, subscapular skinfold and percent body fat estimated from the sum of four skinfolds). Estimates of sensitivity, specificity, predictive value and efficiency were used to describe the relative validity of the anthropometric indicators, and the nature of misclassification resulting when the indicators were applied. The indicators were characterized generally by low levels of sensitivity and corresponding high rates of false negatives, i.e. truly obese youths who were considered not obese by the indicators. Although indicators had high specificities, there were significant differences among indicators. The general pattern of high specificity is desirable, given the nature of obesity in youths. Using the validity criteria and conventional referent values, triceps skinfold thickness in boys and BMI in girls are the preferred single anthropometric indicators of obesity in youths.