Table 2—
Smoking habits
Group 1
Group 2
Group 3
Total
Cigarettes/day
20
21
20
20
Pack-yrs
21.72
16.19
16.18
18.47
FTND
5
5
6
6
Mean age at starting smoking
15
17
16
16
FTND: Fagerström Test of Nicotine Dependence.