CXCL8 and myalgic encephalomeyelitis/chronic fatigue syndrome: Subjects would be assigned to the ME/CFS class if 0 < α0 + α1× [IL-1a] + α2 × [IL-6] + α3 × [IL-8], where [x] is the z score normalized concentration of cytokine x based on the mean and standard deviation values listed in Additional file 1: Table S3.