Table 5

Relative risk (RR) with 95% confidence interval (95% CI) of developing seropositive rheumatoid arthritis for 18–70 years old female and male subjects who have smoked cigarettes for ⩾20 years compared with never-smokers by intensity of smoking

Number of cigarettes
smoked a day
Number of exposed casesRR*95% CI
*Relative risk adjusted for age, residential area, and sex.
1–5151.60.7 to 3.7
6–9242.51.3 to 4.7
10–191033.02.0 to 4.6
⩾20752.41.5 to 3.7