Baseline characteristics of RA cases and controls in the earlier (incidence 1996–2000) and later (incidence 2001–2006) cohorts
| Characteristic | Controls 1996–2000 cohort (n=10 798) | RA 1996–2000 cohort (n=10 798) | RA vs controls p Value | Controls 2001–2006 cohort (n=14 116) | RA 2001–2006 cohort (n=14 116) | RA vs controls p Value |
|---|---|---|---|---|---|---|
| Female, n (%) | 7162 (66.33) | 7162 (66.33) | 1.000 | 9398 (66.58) | 9398 (66.58) | 1.000 |
| Age at index date | 58.34 (17.39) | 58.35 (17.38) | 0.983 | 57.49 (16.88) | 57.49 (16.88) | 0.978 |
| RA duration at index date*, years, median (25Q;75Q) | N/A | 0.63 (0.27;2.35) | N/A | 0.36 (0.23;0.90) | ||
| Romano Charlson comorbidity index†‡ | 0.36 (1.07) | 0.38 (0.98) | 0.200 | 0.36 (1.08) | 0.37 (0.96) | 0.215 |
| Hospitalisation rate per year§¶ | 0.22 (0.34) | 0.28 (0.40) | <0.001 | 0.19 (0.29) | 0.23 (0.31) | <0.001 |
| Cumulative no. of hospitalised days§¶ | 14.59 (78.08) | 14.36 (51.12) | 0.794 | 12.47 (62.77) | 12.66 (29.22) | 0.744 |
| Diabetes‡, n (%) | 605 (5.60) | 586 (5.43) | 0.571 | 956 (6.77) | 907 (6.43) | 0.240 |
| COPD‡, n (%) | 668 (6.19) | 813 (7.53) | <0.001 | 718 (5.09) | 940 (6.66) | <0.001 |
| Renal failure‡, n (%) | 72 (0.67) | 78 (0.72) | 0.623 | 144 (1.02) | 145 (1.03) | 0.953 |
| Any CVD‡, n (%) | 4115 (38.11) | 4392 (40.67) | <0.001 | 5724 (40.55) | 6115 (43.32) | <0.001 |
| Prior CVA¶, n (%) | 754 (6.98) | 831 (7.70) | 0.045 | 1053 (7.46) | 991 (7.02) | 0.154 |
| Prior AMI¶, n (%) | 536 (4.96) | 548 (5.08) | 0.708 | 698 (4.94) | 721 (5.11) | 0.531 |
| Prior cancer¶, n (%) | 1378 (12.76) | 1391 (12.88) | 0.791 | 2036 (14.42) | 2078 (14.72) | 0.479 |
| Prior hospitalised infection¶, n (%) | 839 (7.77) | 1094 (10.13) | <0.001 | 1181 (8.37) | 1531 (10.85) | <0.001 |
Unless otherwise indicated, values represent mean (SD); p values are from χ2 for binary variables, or two-sample t-test for continuous variables.
*RA duration at index date was calculated as time from first RA visit to index date (ie, second RA visit at least 8 weeks later).
†Romano Charlson refers to the Romano adaptation of the Charlson comorbidity index developed for use with administrative health data, excluding RA as a comorbidity.67–69
‡Assessed over 1 year prior to index date.
§Hospitalisation rate was calculated as the number of hospitalisation events per year; cumulative number of hospitalised days was calculated as the sum of all days spent in hospital during all hospitalisations.
¶Assessed over all available data preindex date, that is, from 1990 onwards.
25Q;75Q, 25th and 75th percentile; AMI, acute myocardial infarct; COPD, chronic obstructive pulmonary disease; CVA, cerebrovascular accident; CVD, cardiovascular disease.