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) | |||
| Never | 1.0 | |||
| [66] | 165 | 178 | Current | 0.95 (0.6–1.6) |
| Ex | 1.7 (0.95–3.1) | |||
| Never | 1.0 | |||
| [79] | 7697 | 370,000 | Current | 1.2 (1.1–1.3) |
| Ex | 1.0 (0.95–1.1) | |||
| Never | 1.0 | |||
| [67] | 361 | 5851 | Current (males) | 2.4 (1.5–3.9) |
| Current (females) | 1.1 (0.8–1.6) | |||
| Never | 1.0 |