Characteristics of the EIRA RA cases from 1995 to 2016 and population controls at enrolment questionnaire
| Characteristic | RA cases (N=3515) | Controls (N=5429) | Adjusted OR* for all RA (95% CI) |
| Age, years, median (Q1,Q3) | 55 (45,63) | 56 (44,63) | 1.00 (0.99 to 1.00) |
| Female sex, N (%) | 2493 (71) | 3838 (71) | 1.05 (0.95 to 1.16) |
| BMI, kg/m2, N (%) | |||
| <20 | 252 (7) | 320 (6) | 1.23 (1.03 to 1.48) |
| 20–25 | 1574 (45) | 2576 (48) | (ref) |
| 25–30 | 1178 (34) | 1811 (34) | 1.04 (0.94 to 1.15) |
| 30+ | 502 (14) | 699 (13) | 1.12 (0.98 to 1.28) |
| Educational level, N (%) | |||
| Compulsory school only | 876 (25) | 1043 (19) | (ref) |
| Upper secondary school | 1803 (51) | 2649 (49) | 0.80 (0.71 to 0.89) |
| University degree | 835 (24) | 1730 (32) | 0.61 (0.53 to 0.69) |
| Smoking status, N (%) | |||
| Never smoker | 1146 (33) | 2413 (45) | (ref) |
| Non-regular smoker | 287 (8) | 478 (9) | 1.26 (1.07 to 1.49) |
| Past smoker | 1146 (33) | 1562 (29) | 1.56 (1.40 to 1.73) |
| Current smoker | 915 (27) | 924 (17) | 1.95 (1.73 to 2.19) |
*Adjusting for age, sex, BMI, education, smoking. Bold values are statistically significant (p<0.05).
BMI, body mass index; EIRA, Epidemiological Investigation of Rheumatoid Arthritis; RA, rheumatoid arthritis.