Characteristics of the patients with rheumatoid arthritis and controls studied
| Patients | Controls | |
| Number | 239 | 239 |
| Sex (No (%)) | ||
| Male | 79 (33) | 79 (33) |
| Female | 160 (67) | 160 (67) |
| Age (years) | ||
| Mean (SD) | 60.5 (11.8) | 60.5 (11.8) |
| Age at onset (years) | ||
| Mean (SD) | 46.9 (13.2) | NA |
| Disease duration (years) | ||
| Mean (SD) | 13.6 (9.9) | NA |
| Social class (No (%)) | ||
| Classes I–II | 29 (12) | 29 (12) |
| Classes IIIN–IIIM | 86 (36) | 86 (36) |
| Classes IV–V | 124 (52) | 124 (52) |