Characteristics of participating cases and controls in the EIRA
| RA cases | ||||
|---|---|---|---|---|
| RA overall | ACPA-positive | ACPA-negative | Controls | |
| (n=3150) | (n=2094) (66%) | (n=1056) (34%) | (n=5130) | |
| Age, mean±SD | 51±12 | 51±12 | 52±12 | 52±13 |
| Female (%) | 2252 (71) | 1514 (72) | 738 (70) | 3655 (71) |
| BMI≥25 (%) | 1482 (47) | 944 (45) | 538 (51) | 2324 (45) |
| Smoking status (%) | ||||
| Never | 1023 (32) | 624 (30) | 399 (38) | 2301 (45) |
| Ever | 2113 (67) | 1461 (70) | 652 (62) | 2779 (54) |
| Smoking intensity (%) | ||||
| <10 pack-years | 638 (20) | 421 (20) | 217 (21) | 1095 (21) |
| 10–19 pack-years | 535 (17) | 379 (18) | 156 (15) | 642 (13) |
| ≥20 pack-years | 715 (23) | 531 (25) | 184 (17) | 682 (13) |
| University degree (%) | 807 (26) | 528 (25) | 279 (26) | 1768 (34) |
| Drinking alcohol (%) | ||||
| Non-drinkers | 260 (8) | 177 (8) | 83 (8) | 291 (6) |
| Low | 1618 (51) | 1092 (52) | 526 (50) | 2282 (44) |
| Moderate | 743 (24) | 480 (23) | 263 (25) | 1287 (25) |
| High | 513 (16) | 330 (16) | 183 (17) | 1202 (23) |
| Silica exposed (%) | 147 (5) | 99 (5) | 48 (5) | 162 (3) |
| Work status at baseline (%) | ||||
| Working | 2377 (75) | 1604 (77) | 773 (73) | 4023 (78) |
| Not working | 645 (20) | 401 (19) | 244 (23) | 811 (16) |
| Missing information* | 128 (4) | 89 (4) | 39 (4) | 296 (6) |
| Work status 5 years before baseline (%) | ||||
| Working | 2895 (92) | 1920 (92) | 975 (92) | 4591 (89) |
| Not working | 129 (4) | 87 (4) | 42 (4) | 242 (5) |
| Missing information* | 126 (4) | 87 (4) | 39 (4) | 297 (6) |
Missing with <2% was not shown.
One pack-year of smoking is equivalent to smoking 20 cigarettes per day for 1 year; alcohol consumption was measured in drinks/week (1 drink=16 g) and categorised based on the alcohol consumption distribution of the controls.
Low (≤median), moderate (≥median and ≤75th centile), high (≥75th centile).
*These are individuals with missing information on occupational physical workload exposures.
ACPA, anticitrullinated protein antibody; BMI, body mass index; EIRA, Epidemiological Investigation of Rheumatoid Arthritis; RA, rheumatoid arthritis.