Published estimates of CD4 cell count decay rate and variability in untreated HIV-infected individuals.

Parameters derived from linear mixed effect model in the square root scale. β: slope and σb: inter-individual slope variability in (106/L)0.5/year; α: intercept, σa: inter-individual intercept variability and σe: intra-individual variability in (106/L)0.5; ρab: correlation between α and β; N: number of individuals, n: average number of samples per individual; average duration of observation in years.*slope according to age (15–20: 1.30, 20–30: 1.53, 30–40: 1.73, >40: 1.67) and to symptoms at pre-infection (present: +0.26).°intercept depending on subgroup (sex, age, intravenous drug use or haemophilia).†slope depending on viral load (0 at 3, then 0.016, 0.04, 0.12, 0.4, 0.8 and 1.6 for every 100.5 step up to 2.0 at >106/mL), age (+0.007/year), X4-virus shift (present: +0.25).‡slope depending on age (35: 2).**standard deviation of an uniform distribution in the untransformed CD4 count scale.°°outlier value discarded from average calculation.