The objective of this study was to determine the accuracy, precision, bias, and reliability of percent fat (%fat) determined by air-displacement plethysmography (ADP) with the pediatric option against the four-compartment model in 31 children (4.1 +/- 1.2 years, 103.3 +/- 10.2 cm, 17.5 +/- 3.4 kg). %Fat was determined by (BOD POD Body Composition System; COSMED USA, Concord, CA) with the pediatric option. Total body water (TBW) was determined by isotope dilution ((H2O)-H-2; 0.2g/kg) while bone mineral was determined by dual-energy X-ray absorptiometry (DXA) (Lunar iDXA v13.31; GE, Fairfield, CT and analyzed using enCore 2010 software). The four-compartment model by Lohman was used as the criterion measure of % fat. The regression for % fat by ADP vs. % fat by the four-compartment model did not deviate from the line of identity where: y = 0.849(x) + 4.291. ADP explained 75.2% of the variance in % fat by the four-compartment model while the standard error of the estimate (SEE) was 2.09 % fat. The Bland-Altman analysis showed % fat by ADP did not exhibit any bias across the range of fatness (r = 0.04; P = 0.81). The reliability of ADP was assessed by the coefficient of variation (CV), within-subject SD, and Cronbach's alpha. The CV was 3.5%, within-subject SD was 0.9%, and Cronbach's a was 0.95. In conclusion, ADP with the pediatric option is accurate, precise, reliable, and without bias in estimating % fat in children 2-6 years old.
