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 cumulative dose of smoking
| Number of pack-years | Number of exposed cases | RR* | 95% CI |
|---|---|---|---|
| *Relative risk adjusted for age, residential area, and sex. | |||
| <10 | 65 | 1.0 | 0.7 to 1.5 |
| 10–19 | 78 | 1.8 | 1.2 to 2.6 |
| ⩾20 | 136 | 2.7 | 1.8 to 3.9 |