NHANES (CDC), derived BRI percentiles
About this reference
FitnessNorms calculated Body Roundness Index from NHANES waist circumference and standing height using the Thomas et al. (2013) formula, then calculated weighted empirical P5, P25, P50, P75, and P95 values within sex and five-year age brackets. Adults with complete inputs were included and participants recorded as pregnant were excluded, leaving n=5,718. MEC examination weights were applied. The published table uses the 2021-2023 release. A duration-adjusted 2015-2023 pool was retained as a sensitivity analysis: 71 of 130 cells differed from the recent release by more than 0.15 BRI units, the median absolute difference was 0.160, and the maximum was 1.90. Those differences do not by themselves identify a cause. The recent release is therefore published without describing the pool as an estimate of the same population. Survey-design standard errors were not calculated.
Known limitations
- US adults only. These values should not be assumed to represent other countries or measurement protocols.
- This is an internal derivation from public microdata, not a peer-reviewed percentile publication. Weighted empirical quantiles are reported without survey-design standard errors.
- The single-release sample is smaller than a multi-period pool, so tail estimates within individual cells are less stable. Cell sizes range from 136 to 397.
- Known pregnancies were excluded using RIDEXPRG. That variable identifies pregnancy status only where NHANES reports it and does not exclude postpartum participants.
- RIDAGEYR is top-coded at 80 in the public release, so the 80+ bracket cannot show variation within older ages.
- Cross-sectional age differences do not show how an individual's BRI changes over time, and the sensitivity comparison cannot separate population change, sampling variation, and nonlinear formula effects.
- No single widely accepted clinical BRI threshold exists; these are distribution percentiles rather than diagnostic boundaries.