Characteristics of ankylosing spondylitis (AS) and comparison cohorts at baseline
| Variable* | AS N=7190 | Non-AS N=71 900 | P value |
| Age, mean (SD) | 45.79 (15.6) | 45.78 (15.62) | 0.959 |
| Female | 3501 (48.7) | 35 010 (48.7) | 1.000 |
| Obesity | 31 (0.4) | 197 (0.3) | 0.027 |
| Alcoholism with liver disease | 71 (1) | 574 (0.8) | 0.098 |
| Hypertension | 1091 (15.2) | 10 222 (14.2) | 0.028 |
| Sepsis | 12 (0.2) | 61 (0.1) | 0.039 |
| Varicose veins | 57 (0.8) | 510 (0.7) | 0.420 |
| Inflammatory bowel disease | 225 (3.1) | 241 (0.3) | <0.001 |
| Trauma | 14 (0.2) | 147 (0.2) | 1.000 |
| Fractures | 126 (1.8) | 837 (1.2) | <0.001 |
| Surgery | 74 (1) | 395 (0.5) | <0.001 |
| Charlson Comorbidity Index, mean (SD) | 0.49 (0.94) | 0.23 (0.83) | <0.001 |
| Glucocorticoids | 1154 (16.1) | 2422 (3.4) | <0.001 |
| Hormone replacement therapy | 377 (5.2) | 2484 (3.5) | <0.001 |
| Oral contraceptives | 401 (5.6) | 3371 (4.7) | 0.001 |
| Aspirin | 79 (1.1) | 613 (0.9) | 0.039 |
| Cyclooxygenase-2 inhibitors | 1391 (19.3) | 1834 (2.6) | <0.001 |
| Hospitalised | 1489 (20.7) | 8838 (12.3) | <0.001 |
| No of outpatient visits, mean (SD) | 16.78 (14.18) | 7.63 (10.13) | <0.001 |
Values are N (percentages) unless otherwise noted.
*All variables were calculated in the year before prior to cohort entry.