Table 8. Joint effect on lung cancer risk of smoking (2 strata) and cancer among first-degree relatives (2 strata), by gender and age.

	Smoking (pack-years)	Cancer in relatives1	Cases (n = 334)	Controls (n = 578)	OR2 (95% CI)
GENDER
Males	0 – 20	No3	29	120	1.00
		Yes	4	29	0.50 (0.16 – 1.56)
	≥ 21	No	148	163	3.84 (2.39 – 6.16)
		Yes	66	45	5.50 (3.13 – 9.68)
Females	0 – 20	No3	38	130	1.00
		Yes	11	42	0.93 (0.43 – 2.04)
	≥ 21	No	15	16	3.25 (1.42 – 7.42)
		Yes	10	7	4.89 (1.68 – 14.25)
AGE
< 60 years	0 – 20	No3	30	122	1.00
		Yes	7	27	1.00 (0.39 – 2.56)
	≥ 21	No	72	100	3.66 (2.07 – 6.46)
		Yes	27	24	4.96 (2.45 – 10.07)
≥ 60 years	0 – 20	No3	37	128	1.00
		Yes	8	44	0.62 (0.27 – 1.45)
	≥ 21	No	91	79	3.86 (2.25 – 6.63)
		Yes	49	28	5.74 (2.97 – 11.09)

¹Parents and siblings

²Odds ratio adjusted for age, gender and socioeconomic status (four levels)

³Reference category.