Graphical representation of hypervariable (HV) gene analysis in patients with juvenile rheumatoid arthritis (JRA) (n = 9) and a reference group (n = 12). A reference group of genes from the control group whose expression levels do not vary significantly on a population basis was identified as described in Materials and methods. Expression levels in this reference group, denoted the averaged profile, have a normal distribution. This group is represented by black lines on a plot of residuals (values representing expression level variance in the control population) vs average gene expression levels (log10-transformed). Red lines represent genes whose variation in expression in healthy controls or untreated patients with acute disease was significantly greater than that of the reference group. These genes are defined as hypervariable (HV) genes.