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Table 1 Characteristics of included cases and controls

From: Abdominal obesity, gender and the risk of rheumatoid arthritis – a nested case–control study

  Cases (n = 557) Controls (n = 1671)
Female sex, n (%) 379 (68) 1137 (68)
Data from the health examination visit
 Age at examination (years), mean (SD) 51.9 (9.1) 51.9 (9.1)
 Body mass index (kg/m2), mean (SD) 26.3 (4.3) 25.9 (4.0)
 BMI category, n (%)
  Underweight 5 (0.9) 15 (0.9)
  Normal weight 220 (39.7) 748 (45.3)
  Overweight 231 (41.7) 661 (40.1)
  Obese 98 (17.7) 226 (13.7)
 Smoking habits, n (%)
  Non-smoker 177 (32.2) 812 (49.6)
  Ex-smoker 175 (31.9) 498 (30.4)
  Smoker 197 (35.9) 327 (20.0)
 Educational level, n (%)
  9 years or less 219 (39.8) 538 (32.8)
  10–12 years 239 (43.5) 757 (46.1)
  More than 12 years 92 (16.7) 346 (21.1)
 Waist circumference (cm), mean (SD) (sample sizea: cases n = 138, controls n = 409) 92 (14) 89 (12)
 Abdominal obesityb, n (%) (sample sizea: cases n = 138, controls n = 409) 54 (39.1) 131 (32.0)
 Positive ACPA at examination, n (%) (sample sizec: cases n = 476, controls n = 800) 179 (37.6) 20 (2.5)
Data from the time point of RA symptom onset or later (only cases)
 Time between the health examination visit and the onset of RA symptom (years)   
  Mean (SD) 6.4 (4.5)  
  Median (Q1, Q3) 5.5 (2.9, 8.9)  
 Age at RA symptom onset (years), mean (SD) 58.3 (10.5)  
 Positive ACPA at/after RA diagnosis, n (%) (sample sizec: cases n = 473) 380 (80.4)  
 Positive RF at/after RA diagnosis, n (%) (sample sizec: cases n = 552) 434 (78.6)  
 Positive ACPA and/or RF at/after RA diagnosis, n (%) (sample sizec: cases n = 554) 474 (85.6)  
  1. aWaist circumference was measured in the MONICA cohort, and was introduced as a measurement in the VIP cohort 2004. bAbdominal obesity was defined as waist circumference >102 cm (men) or >88 cm (women). cACPA analysed in blood samples from the health examination was available for 476 cases and 800 controls. Anti-citrullinated peptide antibodies (ACPA) or rheumatoid factor (RF) at/after rheumatoid arthritis (RA) diagnosis was available for 473 cases and 552 cases, respectively, and either ACPA or RF at/after diagnosis was available for 554 cases. SD standard deviation, BMI body mass index