Carrier frequency comparisons of the different HLA-DRB1 allele groups between rheumatoid arthritis (RA) cases and controls across the various Caucasoid and non-Caucasoid population samples and overall effect estimation. This figure provides a summary meta-analysis of allele carrier frequencies according to HLA-DRB1 allele classification, in selected samples among the data available from the 13th International Histocompatibility Working Group on Rheumatoid Arthritis. For each population sample, odds ratios (ORs) and 95% confidence intervals (95% CIs) evaluate the significance of the association between the different HLA-DRB1 allele groups and RA susceptibility (blue boxes). The combined ORs and 95% CIs evaluate the significance of the global effect of the different HLA-DRB1 allele groups on RA susceptibility over all population samples. P values were calculated with the Mantel-Haenszel method (black diamonds).