Table 1
Cases and controls stratified by exacerbation frequency and smoking status
Never/ex-smoker
Active smoker
Total
COPD
Group 1 (no exacerbations)
12
4
16
Group 2 (⩽2 exacerbations/year)
12
4
16
Group 3 (>2 exacerbations/year)
15
0
15
Controls
40
8
48