Table 1– Summary of cross-sectional studies that compared clinical characteristics in chronic obstructive pulmonary disease subjects with and without chronic cough and sputum production

First author [ref.]	Population	Subjects n	Chronic cough and/or sputum	Current smokers		Exacerbations per patient per year		Dyspnoea MMRC scale		HRQoL
First author [ref.]	Population	Subjects n	Chronic cough and/or sputum	Cough + sputum	No cough + sputum	Cough + sputum	No cough + sputum	Cough + sputum	No cough + sputum	Cough + sputum	No cough + sputum
Agusti [2]	Clinic based (multinational)	2161	34.6	GOLD 2: 52* GOLD 3: 46* GOLD 4: 37*	GOLD 2: 31 GOLD 3: 3 GOLD 4:21	GOLD 2: 0.6±1.1 GOLD 3: 1.0±1.2 GOLD 4: 1.2±1.6	GOLD 2: 0.7±1.0 GOLD 3: 1.0±1.4 GOLD 4: 1.2±1.3	GOLD 2: 1.5±1.0* GOLD 3: 1.8±1.0 GOLD 4: 2.4±1.0	GOLD 2: 1.3±1.0 GOLD 3: 1.8±1.1 GOLD 4: 2.3±1.0	SGRQ-C GOLD 2:50.3±18.8* GOLD 3: 58.8±17.6* GOLD 4:65.0±16.5*	SGRQ-C GOLD 2:38.9± 20.5 GOLD 3:51.2±18.2 GOLD 4:59.4±15.2
Burgel [15]	Clinic based (France)	433	74.1	28*	18	2.2±2.2*	1.0±1.2	N/A	N/A	N/A	N/A
Kim [16]	Clinic-based (USA)	1061	27.3	48*	27	1.2±1.6*	0.63±1.1	3 (2–4)*	2 (1–3)	SGRQ 62.5±19.0*	SGRQ 38.0±22.4
Montes de Oca [14]	Population based (Latin America)	759	14.4^#	47*	32	5.42	2.66	Present: 76*	Present: 47	SF-12 physical score 44.6±1.01*	SF-12 physical score 49.5±0.36
Lu [17]	Population based (China)	1668	30.0	48*	37	N/A	N/A	MMRC >2: 64*	MMRC >2: 29	N/A	N/A

Data are presented as %, mean±sd or median (interquartile range), unless otherwise specified. MMRC: modified Medical Research Council; HRQoL: heath-related quality of life; GOLD: Global initiative for chronic Obstructive Lung Disease; SGRQ: St. George's Respiratory Questionnaire; SGRQ-C: chronic obstructive pulmonary disease version of the SGRQ; N/A: not applicable; SF-12: Short Form-12 questionnaire. ^#: phlegm most days, at least 3 months a year for ≥2 yrs. *: p<0.05.