CD4 and AIDS: We demonstrate the use of the statistical methods developed through a reanalysis of the dataset of pre‐ART CD4 counts described by Babiker et al., 3, comprising all available measurements prior to the occurrence of acquired immune deficiency syndrome (AIDS)‐defining illness or initiation of ART up to December 2007 from 21 cohorts (originating from 12 countries) participating in the Concerted Action on SeroConversion to AIDS and Death in Europe (CASCADE) study 17.