Table 2 Correlations between symptoms and patient characteristics

	n	Morning symptoms^a		Night symptoms^b
		r	Proportion explained variance (r²)	r	Proportion explained variance (r²)
Characteristics
Age	2,233	−0.12	1%	−0.1	1%
Age of onset	1,992	−0.05	0%	−0.02	0%
FEV₁ predicted	2,227	−0.16	3%	−0.1	1%
FEV₁/FVC predicted	2,224	−0.11	1%	−0.03	0%
Mean number of exacerbations last year	2,228	0.13	2%	0.12	1%
Symptoms
Night symptoms (ACQ question 1)	2,233	0.53	28%	1	100%
Morning symptoms (ACQ question 2)	2,231	1	100%	0.53	28%
Sputum production (CCQ question 6)	2,231	0.46	21%	0.39	15%
Wheezing (ACQ question 5)	2,232	0.45	20%	0.44	19%
Health status
CCQ subscale functional status	2,233	0.44	19%	0.39	15%
CCQ subscale mental status	2,230	0.41	17%	0.39	15%
CCQ subscale symptoms	2,232	0.59	35%	0.52	27%
CCQ total scale	2,229	0.58	34%	0.52	27%

Abbreviations: ACQ, Asthma Control Questionnaire; CCQ, COPD Clinical Questionnaire; COPD, chronic obstructive pulmonary disease; FEV₁, forced expiratory volume in 1 s; FVC, forced vital capacity.
^aACQ question 2.
^bACQ question 1.

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