Equations for predicted values for the median (M), the variability around the median (S) and the skewness (L) for each of the test indices are presented for all data. Mspline and Sspline correspond to the age-varying coefficients from the look-up tables available in the supplementary material or for download from the Global Lung Function Initiative website: www.lungfunction.org
| Sex | Median (M) | Variability around the median (S) | Skewness (L) | |
| FRC | Male | exp(−13.4898+0.1111*log(age)+2.7634*log(height)+Mspline) | exp(−1.60197+0.01513*log(age)+Sspline) | 0.3416 |
| Female | exp(−12.7674+0.1251*log(age)+2.6049*log(height)+Mspline) | exp(−1.48310–0.03372*log(age)+Sspline) | 0.2898 | |
| TLC | Male | exp(−10.5861+0.1433*log(age)+2.3155*log(height)+Mspline) | exp(−2.0616143–0.0008534*age+Sspline | 0.9337 |
| Female | exp(−10.1128+0.1062*log(age)+2.2259*log(height)+Mspline) | exp(−2.0999321+0.0001564*age+Sspline) | 0.4636 | |
| RV | Male | exp(−2.37211+0.01346*age+0.01307*height+Mspline) | exp(−0.878572–0.007032*age+Sspline) | 0.5931 |
| Female | exp(−2.50593+0.01307*age+0.01379*height+Mspline) | exp(−0.902550–0.006005*age+Sspline) | 0.4197 | |
| RV/TLC | Male | exp(2.634+0.01302*age–0.00008862*height+Mspline) | exp(−0.96804–0.01004*age+Sspline) | 0.8646 |
| Female | exp(2.666+0.01411*age–0.00003689*height+Mspline) | exp(−0.976602–0.009679*age+Sspline) | 0.8037 | |
| ERV | Male | exp(−17.328650–0.006288*age+3.478116*log(height)+Mspline) | exp(−1.307616+0.009177*age) | 0.5517 |
| Female | exp(−14.145513–0.009573*age+2.871446*log(height)+Mspline) | exp(−1.54992+0.01409*age) | 0.5326 | |
| IC | Male | exp(−10.121688+0.001265*age+2.188801*log(height)+Mspline) | exp(−1.856546+0.002008*age) | 1.146 |
| Female | exp(−9.4438787–0.0002484*age+2.0312769*log(height)+Mspline) | exp(−1.775276+0.002673*age) | 0.9726 | |
| VC | Male | exp(−10.134371–0.003532*age+2.307980*log(height)+Mspline) | exp(−2.1367411+0.0009367*age | 0.8611 |
| Female | exp(−9.230600–0.005517*age+2.116822*log(height)+Mspline | exp(−2.220260+0.002956*age | 1.038 |
FRC: functional residual capacity; TLC: total lung capacity; RV: residual volume; ERV: expiratory reserve volume; IC: inspiratory capacity; VC: vital capacity.