Table 4

Relative risk (RR) with 95% confidence interval (95% CI) of developing seropositive rheumatoid arthritis for 18–70 years old female and male ever-smokers compared with never-smokers by duration of smoking

Number of years
of smoking
Number of exposed casesRR*95% CI
*Relative risk adjusted for age, residential area, and sex.
<10260.80.4 to 1.4
10–19360.80.5 to 1.3
⩾202172.61.8 to 3.6