CD4 and AIDS: For CD4, in contrast, the prognostic risk at the lower 75th centile compared to the ‘median’ patient, rose markedly with decreasing median CD4: from 1.0 (i.e., no prognostic information) at CD4s above 625/μL – which, in our dataset, corresponded to the time of seroconversion – to maxima of 6.3 (95% CI 4.4–8.9) for AIDS and 5.5 (95% CI 2.7–10.1) for death in populations with median 300 CD4/μL – which, in the dataset of prognostic risks, corresponded to around 6 years after seroconversion (Figure 3b).