Table 4. Cox regression of overall mortality in patients starting long-term oxygen therapy, 1992–2008.

Characteristic	Hazard ratio	95% confidence interval	P-value
Age	1.04	1.04–1.04	<0.001
Female	0.73	0.68–0.77	<0.001
PaO2 air	0.88	0.86–0.91	<0.001
FEV1	0.82	0.76–0.88	<0.001
Past smoking*	1.05	0.94–1.20	0.356
Current smoking*	1.33	1.07–1.64	0.010
Start year	1.00	1.00–1.01	0.391
Charlson score†
1	1.14	1.07–1.22	<0.001
2	1.39	1.26–1.52	<0.001
3	1.52	1.32–1.75	<0.001
>3	1.69	1.42–2.02	<0.001
Anemia	1.28	1.10–1.48	0.001
Arrhythmia	1.23	1.13–1.34	<0.001
Mental disorder	1.18	1.06–1.32	0.003
Osteoporosis	1.31	1.17–1.48	<0.001

Definition of abbreviations: FEV₁ = forced expiratory volume in one second; Pa_O2 air = arterial blood gas tension of oxygen while breathing ambient air.

^*Never smoking is used as reference category.

^†Charlson score 0 is used as reference category.