Phi coefficient ranging from -1 to 1 and related P values were calculated for JIA as a group (Supplementary Fig. 2). For the JIA group there was a strong significant positive correlation between HLA-DRB1*08 and HLA-DQA1*04 (phi = 0.97, P < 0.0001), HLA-DQB1*04 (phi = 0.95, P < 0.0001). This evidence concerns the gene HLA-DRB1 and juvenile idiopathic arthritis.