	Coef (95% CI)	P value	AIC	Coef (95% CI)	P value	AIC
MMRC	−0.026 (−0.027 to 0.025)	<0.001	3150	−0.026 (−0.027 to 0.025)	<0.001	3065
SGRQ	−0.44 (−0.46 to 0.43)	<0.001	57 014	−0.45 (−0.46 to 0.43)	<0.001	56 967
Emphysema, %*	−0.23 (−0.24 to 0.22)	<0.001	22 926	−0.24 (−0.25 to 0.23)	<0.001	22 827
Gas trapping, %*†	−0.52 (−0.53 to 0.50)	<0.001	25 519	−0.52 (−0.53 to 0.5)	<0.001	25 471
6-MWD, feet	6.35 (6.07 to 6.64)	<0.001	114 300	6.61 (6.3 to 6.9)	<0.001	1 14 144

All regression models included the following covariates: age, sex, race, smoking status, pack per years, history (per questionnaire) of asthma, diabetes, high blood pressure, stroke and sleep apnoea.
*For emphysema and gas trapping analysis, data were available for 5553 and 4945 subjects, respectively.
†Gas trapping was measured at functional residual capacity.
6-MWD, 6 min walk distance; AIC, Akaike information criterion; FEV₁, forced expiratory volume in 1 s; FVC, forced vital capacity; MMRC, modified Medical Research Council dyspnoea score; SGRQ, St. George’s Respiratory Questionnaire score.