Table 2 Summary of recent epidemiological studies showing the association between rheumatoid arthritis and cigarette smoking
Study | Cases (n) | Controls (n) | Smoking group | Odds ratio (95% confidence interval) |
[78] | 239 | 239 | 41–50 pack years | 13.5 (2.9–63.4) |
|  |  |  | Ever | 1.8 (1.2–2.2) |
| Â | Â | Â | Never | 1.0 |
[66] | 165 | 178 | Current | 0.95 (0.6–1.6) |
|  |  |  | Ex | 1.7 (0.95–3.1) |
| Â | Â | Â | Never | 1.0 |
[79] | 7697 | 370,000 | Current | 1.2 (1.1–1.3) |
|  |  |  | Ex | 1.0 (0.95–1.1) |
| Â | Â | Â | Never | 1.0 |
[67] | 361 | 5851 | Current (males) | 2.4 (1.5–3.9) |
|  |  |  | Current (females) | 1.1 (0.8–1.6) |
| Â | Â | Â | Never | 1.0 |