Characteristics of cases and controls
| ACPA-positive cases | ACPA-negative cases | Controls | |
| Exposed to passive smoking, n (%) | 180 (47) | 98 (48) | 876 (50) |
| Women, n (%) | 301 (78) | 137 (67) | 1293 (73) |
| Men, n (%) | 84 (22) | 67 (33) | 471 (27) |
| Scandinavian, n (%) | 333 (86) | 185 (91) | 1533 (87) |
| Mean age at disease onset (SD) | 52.8 (16.0) | 47.8 (15.3) | |
| Disease duration since first symptom (SD) | 0.8 (1.1) | 0.9 (1.2) | |
| Total, n | 385 | 204 | 1764 |
ACPA, anti-cyclic citrullinated peptide antibodies.