Table 3

 Odds ratios for rheumatoid arthritis (rheumatoid factor positive, rheumatoid factor negative, and overall) for different combinations of silica exposure and cigarette smoking compared with never smokers unexposed to silica

Absence of silica exposureSilica exposure
No of casesOR*95% CINo of casesOR*95% CI
*Adjusted for the potential confounding from age and residential area.
CI, confidence interval; OR, odds ratio; RA, rheumatoid arthritis; RF, rheumatoid factor.
    Never smoked271.031.80.4 to 9.0
    Ever smoked1262.81.5 to 5.1245.42.1 to 14.0
    Never smoked301.010.40.0 to 8.1
    Ever smoked450.40.2 to 1.0131.60.4 to 7.2
Total RA
    Never smoked571.041.10.3 to 4.4
    Ever smoked1711.40.9 to 2.3373.71.7 to 8.1