. Author manuscript; available in PMC: 2021 Jul 2.

Published in final edited form as: Eur Respir J. 2020 Jul 2;56(1):2000011. doi: 10.1183/13993003.00011-2020

Table 3.

Summary of fitted Generalized Additive Mixed Models that model longitudinal log fractional exhaled nitric oxide (logF_ENO₅₀) trajectories as smooth functions of time-varying age and a time-constant covariate plus a participant-level random intercept and random slope on age.

		Males (N=809)			Females (N=908)
Model	Parameter^*	Regression coefficient^**	EDF^†	p-value	Regression coefficient^**	EDF^†	p-value
Age only	s(age)		5.6	<0.0001		5.1	<0.0001

Age and year 3 BMI %	te(age, bmi %)		8.4	<0.0001		7.6	<0.0001

	ti(age)		3.8	<0.0001		3.6	<0.0001
	ti(bmi %)		1.0	0.02		1.0	0.43
	ti(age, bmi %)		1.7	0.009		2.7	0.07

Age and race/ethnicity^‡	Intercept	2.55		<0.0001	2.49		<0.0001
	White/non-Hispanic	−0.07		0.11	−0.06		0.13
	Other	0.16		0.02	0.07		0.21
	s(age)		5.4	<0.0001		5.1	<0.0001
	s(age:Hispanic)		1.6	0.13		0.5	0.23
	s(age:White/non-Hisp)		<0.1	0.31		<0.1	0.51
	s(age:Other)		<0.1	0.70		1.2	0.11

Age and ever reported allergic rhinitis at year 3	Intercept	2.50		<0.0001	2.45		<0.0001
	Allergic Rhinitis	0.15		0.001	0.14		0.0005
	Missing	−0.01		0.83	−0.02		0.70
	s(age)		5.5	<0.0001		5.0	<0.0001
	s(age:None)		<0.1	0.40		<0.1	0.62
	s(age:AllergicRhinitis)		2.7	0.07		<0.1	0.51
	s(age: Missing)		1.0	0.16		<0.1	0.74

Full model	Intercept	2.52		<0.0001	2.46		<0.0001
	White/non-Hispanic	−0.10		0.02	−0.07		0.09
	Other	0.13		0.07	0.05		0.35
	Allergic Rhinitis	0.15		0.001	0.15		0.0004
	Missing	−0.02		0.79	−0.03		0.56
	te(age, bmi %)		8.4	<0.0001		7.6	<0.0001

	Intercept	2.52		<0.0001	2.46		<0.0001
	White/non-Hispanic	−0.10		0.02	−0.07		0.10
	Other	0.13		0.07	0.05		0.35
	Allergic Rhinitis	0.15		0.001	0.15		0.0004
	Missing	−0.02		0.79	−0.03		0.57
	ti(age)		3.8	<0.0001		3.6	<0.0001
	ti(bmi %)		1.0	0.01		1.0	0.40
	ti(age, bmi %)		1.5	0.02		2.7	0.07

Smooth terms definitions: s(): penalized regression spline; ti():tensor product interaction; te():tensor product smooth.

^**

For categorical variables; on logF_ENO₅₀ scale

^†

Effective degrees of freedom (EDF) for the smooth term; a value of 1 indicates a linear effect, higher values indicate a higher degree of non-linearity

^‡

k=5 specified in the s(age, by=race, m=1, k=5) term for improved model convergence