Table 1 Clinical and demographic characteristics of the study subjects

Age (years)

22.0 ± 1.3

Self-reported smoking status

Never

49

Waves 1 to 3 only

23

Wave 4

35

Average cigarette consumption in wave-4 smokers

8 ± 7 per day

Pack year history in wave-4 smokers

≤1 pack year

24

1 to 2 pack years

5

>2 pack years

6

Serum cotinine levels (ng/ml)

<1.0

43

1 < x < 2.0

0

>2.0 ng/ml

64

Average cotinine level in those with cotinine >2 ng/ml

80 ± 58