Table 2

Linear regression model with interactions for predicting square root AEX-FV

 Term Estimate Std error T ratio Prob >|T| VIF Main effect R2 RASE Intercept −0.084 0.007 −11.598 <0.0001 – – T: 0.994 T: 0.074 FVC 0.497 0.002 220.145 <0.0001 2.63 0.24 PEF 0.065 0.002 37.790 <0.0001 6.33 0.20 FEF25 0.096 0.002 47.751 <0.0001 7.41 0.20 FEF50 0.118 0.003 45.661 <0.0001 5.90 0.19 FEF75 0.182 0.005 33.196 <0.0001 4.57 0.16 (PEF-8.75238)·(FEF25-7.10942) −0.003 0.001 −5.385 <0.0001 5.40 (PEF-8.75238)·(FVC-4.11503) −0.002 0.002 −1.448 0.1476 6.74 V: 0.994 V: 0.075 (PEF-8.75238)·(FEF50-3.71047) −0.006 0.002 −2.660 0.0079 22.28 (PEF-8.75238)·(FEF75-1.0233) 0.014 0.005 2.870 0.0041 17.35 (FEF25-7.10942)·(FVC-4.11503) 0.012 0.002 5.441 <0.0001 12.33 (FEF25-7.10942)·(FEF50-3.71047) 0.002 0.002 1.148 0.2510 16.86 (FEF25-7.10942)·(FEF75-1.0233) −0.004 0.005 −0.754 0.4506 20.73 (FVC-4.11503)·(FEF50-3.71047) 0.014 0.003 4.513 <0.0001 11.07 (FVC-4.11503)·(FEF75-1.0233) −0.021 0.005 −3.875 0.0001 6.57 (FEF50-3.71047)·(FEF75-1.0233) −0.019 0.003 −6.096 <0.0001 5.39
• In both training (T, n=2577) and validation (V, n=1057) sets, model’s R2 was ~0.994 and RASE was 0.074–0.075.

• AEX-FV, area under expiratory flow-volume curve; FEF25, forced expiratory flow at 25%; FVC, forced vital capacity; PEF, peak expiratory flow; RASE, root average square error; VIF, variance inflation factor.