Table 1 Characteristics of cases and controls in EIRA and CACORA
CharacteristicEIRACACORA
Cases(n = 1204)Controls(n = 871)p ValueCases(n = 444)Controls(n = 533)p Value
Women (%)73 (n = 879)74 (n = 645)0.5970.3 (n = 312)61.4 (n = 327)0.004
Age (years)*51.1 (12.5)52.1 (11.7)0.0749.1 (11.1)49.8 (10.5)0.31
RA disease duration (years)0.8†2.3‡
ACPA-positive (%)61.1 (n = 735)1.9 (n = 16)<0.00169.4 (n = 308)–¶
Ever smokers (%)66.1 (n = 796)60.3 (n = 525)0.00669.8 (n = 310)60.6 (n = 323)0.003
HLA-DRB1 SE alleles
    Heterozygous carriers (%)49.3 (n = 593)42.8 (n = 373)<0.00145.1 (n = 200)44.5 (n = 237)0.77
    Homozygous carriers (%)24.5 (n = 295)9.8 (n = 85)<0.00130.0 (n = 133)8.4 (n = 45)<0.001
Alcohol consumption
    Non-drinkers (%)15.1 (n = 182)12.5 (n = 109)0.04618.0 (n = 80)10.1 (n = 54)<0.001
    Alcohol intake (drinks/week)*2.9 (4.2)4.1 (5.6)<0.0016.6 (8.9)9.0 (8.7)0.003
    Median (units/week)1.92.945
    75th centile (drinks/week)3.84.98.512
Correlation smoking and alcohol consumption0.11 (p<0.001)0.17 (p<0.001)0.22 (p<0.001)0.17 (p<0.001)
  • *Mean (SD). †Newly diagnosed cases; mean duration between onset of first symptoms and inclusion in the study. ‡Prevalent cases; mean interval between RA diagnosis and inclusion in the study. ¶ACPAs not measured in the controls in CACORA.

  • ACPA, antibodies to citrullinated peptide antigens; CACORA, Case–Control Study on Rheumatoid Arthritis; EIRA, Epidemiological Investigation of Rheumatoid Arthritis; RA, rheumatoid arthritis; SE, shared epitope.