Table 2. Regression coefficients of the final model used to adjust oxygen saturation levels (n = 2,961).

Variable	df	Parameter estimate	Standard error	t value	Pr >|t|
Intercept	1	101.049	1.941
Group*	1	-0.145	0.206	-0.70	0.4824
Sex†	1	-0.390	0.162	-2.40	0.0163
Age	1	0.005	0.005	1.05	0.2952
Smoker‡	1	0.799	0.308	2.59	0.0095
Altitude	1	-0.005	0.0005	-9.32	<.0001
Cough§	1	-0.345	0.288	-1.20	0.2308
Phlegm¶	1	-2.637	4.059	-0.65	0.5158
Sex × cough	1	-0.743	0.393	-1.89	0.0591
Smoker × cough	1	1.755	0.733	2.39	0.0167
Age × phlegm	1	-0.041	0.009	-4.47	<.0001
Altitude × phlegm	1	0.001	0.001	0.90	0.3659

^*0 = No self-reported respiratory symptoms; 1 = reported symptoms.

^†0 = Female; 1 = male.

^‡0 = Nonsmoker; 1 = smoker.

^§0 = No; 1 = yes.

^¶0 = No; 1 = yes.