Table 2.

Backwards selection model^a by Cox regression analysis of predictors for moderate and severe COPD exacerbations for all patients, and by sex

Baseline variable	All patients (n=3,141)		Males only (n=2,017)		Females only (n=1,124)
	HR (95% CI)	Overall P-value	HR (95% CI)	Overall P-value	HR (95% CI)	Overall P-value
Number of COPD maintenance medicationsb
1 vs 0	1.18 (0.98–1.43)	<0.001	1.11 (0.86–1.42)	<0.001	1.33 (0.99–1.77)	<0.001
2 vs 0	1.57 (1.32–1.86)		1.64 (1.31–2.06)		1.50 (1.15–1.96)
3 vs 0	1.91 (1.59–2.30)		1.99 (1.57–2.52)		1.83 (1.35–2.47)
Reliever use, number of inhalations	1.05 (1.04–1.07)	<0.001	1.05 (1.03–1.06)	<0.001	1.05 (1.03–1.08)	<0.001
Number of exacerbations in the previous year
2 vs 1	1.40 (1.21–1.61)	<0.001	1.45 (1.21–1.75)	<0.001
3 vs 1	1.63 (1.33–2.00)		1.74 (1.31–2.31)
4 vs 1	1.70 (1.29–2.24)		1.97 (1.40–2.79)
>4 vs 1	2.07 (1.55–2.78)		2.22 (1.51–3.26)
SGRQ total score					1.01 (1.00–1.02)	<0.001
Pre-bronchodilator FEV1/FVC ratio (per 10%)	0.83 (0.78–0.88)	<0.001	0.98 (0.97–0.99)	<0.01	0.98 (0.97–0.99)	<0.001
Sex, female vs male	1.32 (1.16–1.50)	<0.001

Notes:

^aBackward selection starting with all predictors and recursively removing factors with high P-value until all remaining P-values were <0.001. The number of COPD exacerbations during the previous year was not selected for females alone

^bnumber of COPD maintenance medications at study entry: 0= no maintenance treatment with LA (long-acting β₂-agonists, long-acting antimuscarinics, and theophylline), ICS, or other daily treatments (ie, short-acting [β₂-agonist or antimuscarinic] bronchodilators only), 1= one maintenance medication, 2= two maintenance medications, 3= three or more maintenance medications. Data from.¹⁵–¹⁷

Abbreviations: CI, confidence interval; COPD, chronic obstructive pulmonary disease; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; HR, hazard ratio; ICS, inhaled corticosteroids; LA, long-acting bronchodilator; SGRQ, St George’s Respiratory Questionnaire.