Table 1.
Demographics of cases and controls
| pSS cases invited to questionnaire | pSS cases returning the questionnaire | pSS cases returning the questionnaire and matched to controls | Matched controls | |
|---|---|---|---|---|
| No. of individuals | 815 | 606 | 530 | 4425 |
| % Females | 93 | 93 | 93 | 89 |
| Age at index date (years) | ||||
| Median (IQR) | 53 (42–61) | 54 (41–61) | 54 (43–61) | 54 (42–62) |
| ≤24 | 25 (3%) | 14 (2%) | 13 (2%) | 117 (3%) |
| 25–39 | 137 (17%) | 114 (19%) | 93 (18%) | 795 (18%) |
| 40–54 | 272 (33%) | 197 (33%) | 169 (32%) | 1360 (31%) |
| 55–64 | 222 (27%) | 184 (30%) | 173 (33%) | 1437 (32%) |
| ≥65 | 137 (17%) | 95 (16%) | 82 (15%) | 716 (16%) |
| Calendar year at index date | ||||
| 1980–1985 | 7 (1%) | 6 (1%) | 0 (0%) | 0 (0%) |
| 1985–1990 | 37 (5%) | 23 (4%) | 0 (0%) | 0 (0%) |
| 1990–1995 | 59 (7%) | 42 (7%) | 13 (2%) | 0 (0%) |
| 1995–2000 | 131 (16%) | 97 (16%) | 94 (18%) | 506 (11%) |
| 2000–2005 | 144 (18%) | 112 (18%) | 110 (21%) | 857 (19%) |
| 2005–2010 | 196 (24%) | 161 (27%) | 156 (29%) | 1809 (41%) |
| 2010–2015 | 214 (26%) | 159 (26%) | 154 (29%) | 1253 (28%) |
| 2015–2020 | 3 (0%) | 3 (0%) | 3 (1%) | 0 (0%) |
| Area of residence | ||||
| Bigger cities and Southern Sweden | 609 (75%) | 452 (75%) | 406 (77%) | 3 763 (85%) |
| Middle Sweden | 194 (24%) | 143 (24%) | 115 (22%) | 583 (13%) |
| Northern Sweden | 12 (1%) | 11 (2%) | 9 (2%) | 79 (2%) |
| Highest attained education | ||||
| Primary education (≤9 years) | – | 134 (22%) | 114 (22%) | 1 053 (24%) |
| Secondary education (10– 12 years) | – | 193 (32%) | 172 (32%) | 1 601 (36%) |
| Higher education | – | 274 (45%) | 241 (45%) | 1 764 (40%) |
| SSA and SSB status at the date of pSS diagnosis | ||||
| SSA positive | 563 (69%) | 418 (69%) | 363 (68%) | – |
| SSB positive | 367 (45%) | 269 (44%) | 230 (43%) | – |
| SSA and/or SSB positive | 578 (71%) | 430 (71%) | 375 (71%) | – |
| No. of years between pSS diagnosis and questionnaire response date | ||||
| Median (IQR) | 12 (7–19) | 11 (7–18) | 10 (7–16) | – |
| No. of individuals with HLA data | – | 409 (67%) | 363 (68%) | 2097 (47%) |
HLA, human leucocyte antigen; pSS, primary Sjögren’s syndrome; SSA, Ro/SSA autoantibodies; SSB, La/SSB autoantibodies.