| Cases*n = 163 | Controls†n = 505 | |
| Incorrect address | 12 (7.3) | 179 (34.0) |
| Eligible to respond | 151 (92.6) | 326 (64.5) |
| Non-responders | 26 (17.2) | 163 (50.0) |
| Responders | ||
| initial | 67 (44.3) | 97 (29.8) |
| delayed | 58 (38.4) | 72 (22.1) |
| total | 125 (82.7) | 163 (50.0) |
| Onset of joint symptoms not verified by patient | 27 | – |
| Final group for analysis from eligible subjects | 98 (64.9) | 163 (50.0) |
*Cases: patients with psoriatic arthritis with onset within the past 5 years.
†Controls: patients with psoriasis with no history of inflammatory arthritis.