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.