Table 3

Lung cancer risk in current smokers in relation to smoking duration, cpd, and age at onset of smoking habit

	United States					Japan
		Cases	Hospital Controls	OR (95% CI)	Cases	Hospital Controls	Community Controls	OR (95% CI) (HC; CC)^a
n	148	39		284	115	160
Smoking duration (yr) %
≤40	38.5	56.4	25.2 (11.9–61.0)^b	40.5	71.3	45.0	2.2 (1.1–5.2); 4.8 (2.6–8.9)^c
>40	61.5	43.6	57.8 (27.4–131.9)^b	59.5	28.7	55.0	7.4 (2.9–19.4); 8.3 (4.5–15.4)^c
Mean (SD)	42.6 (10.8)	38.7 (12.3)		41.6 (9.8)	35.4 (9.8)	40.6 (10.3)
cpd %
<20	10.8	38.5	10.9 (4.4–28.0)^b	16.8	29.8	30.6	1.6 (0.7–3.9); 2.6 (1.4–4.9)^c
20–29	35.1	28.2	53.4 (23.1–135.2)^b	35.0	34.2	41.3	3.5 (1.5–8.4); 4.3 (2.4–7.6)^c
≥30	54.1	33.3	73.3 (32.5–181.6)^b	48.2	36.0	28.1	6.2 (2.6–15.0); 9.3 (5.2–16.7)^c,^d
Mean (SD)	30.6 (15.5)	22.9 (16.4)		29.5 (15)	25 (14.8)	22.7 (12.8)
Age at onset of smoking (yr) %
<14	30.4	20.5	1.2 (0.4–3.4)^e	0.7	0.0	0.0	(^f)
15–17	38.5	33.3	1 (reference)^e	21.1	11.3	15.6	1 (reference)^g
18–20	18.2	25.6	0.6 (0.2–1.7)^e	61.6	68.7	60.0	0.2 (0.1–0.6); 0.8 (0.5–1.3)^g
>20	12.8	20.5	0.5 (0.2–1.4)^e	16.6	20.0	24.4	0.2 (0.1–0.8); 0.5 (0.3–0.9)^g,^h
Mean (SD)	16.8 (5.8)	17.8 (5.0)		19.3 (2.9)	20.2 (4.7)	20.5 (5.8)

^a HC, hospital controls; CC, community controls.
^b Adjusted for age, education, and hospital; reference group is nonsmokers.
^c Adjusted for age and education; reference group is nonsmokers.
^d P < 0.001, test for linear trend.
^e Adjusted for age, education and hospital; reference group is 15–17 yrs.
^f ORs were not computed because no current smokers started smoking before the age of 15 in Japanese controls.
^g Adjusted for age and education; reference group is 15–17 yrs.
^h P < 0.01, test for linear trend.