Table 1

Case-referent evaluations of smoking habits in men (102 cases of RA and 248 referents) and women (179 cases of RA and 259 referents) from southeastern Sweden, 1980–95, with adjustment for age and socioeconomic status. ORs from separate analyses of 83 men and 134 women who were rheumatoid factor (RF) positive are also shown. Never users of tobacco are regarded as unexposed

		All cases				Seropositive cases
		Exposed cases/referents	OR^1-150			95% CI^1-150	Exposed cases/referents	OR^1-150	95% CI^1-150
Men
Pack years of smoking^1-151
Non-smokers	20/81	1.0	Reference		14/81	1.0	Reference
<5	2/19	0.4	0.0 to 2.3		1/19	0.2	0.0 to 1.8
5–9	7/22	1.4	0.4 to 4.7		6/22	1.5	0.4 to 5.7
10–19	28/37	2.4	1.0 to 6.1		23/37	2.4	0.9 to 6.6
⩾20	34/44	2.7	1.2 to 5.8		30/44	3.4	1.5 to 8.4
	p for trend <0.010			p for trend <0.005
Women
Pack years of smoking^1-151
Non-smokers	88/145	1.0	Reference		58/145	1.0	Reference
<5	13/16	1.8	0.7 to 4.4		11/16	2.0	0.8 to 5.2
5–9	19/24	1.5	0.7 to 3.2		15/24	1.7	0.7 to 3.9
10–19	21/24	1.5	0.7 to 3.2		17/24	1.8	0.8 to 3.8
⩾20	13/13	1.8	0.7 to 4.6		12/13	2.5	0.9 to 6.7
	p for trend = 0.113			p for trend = 0.029

↵1-150 OR = Mantel-Haenszel odds ratio; CI = confidence interval as outlined by Robins et al.36 ORs are calculated with adjustment for age.
↵1-151 Mean number of packs per day multiplied by the total number of years of smoking.