Table 1. The number of exacerbations, severe exacerbations which need admission to hospital and stay in hospital.

Severity	Exacerbations	Days in hospital	Severe exacerbations which need stay in hospital
Mild	0.87±0.03	2.61±0.17	0.22±0.02
Moderate	1.28±0.01	3.71±0.04	0.52±0.01
Severe	2.73±0.01	7.26±0.05	0.94±0.01
Very severe	3.59±0.02	12.79±0.15	1.77±0.02