Distribution of Lifetime Smoking Exposure (Pack-years)
Group	Pack-years interval	n	%
Never smoked	0	40	47.1
Low (Tertile 1)	(0, 1.7]	15	17.6
Moderate (Tertile 2)	(1.7, 5]	17	20.0
High (Tertile 3)	>5	13	15.3