Fig. 3. Clearance and volume changes with age for pooled analysis. The between-occasion variability for each individual is demonstrated by linking estimates with a fine line. Subjects from the study by Hopkins et al . 6are shown as open squares. (A ) Volume of distribution changes with age up to 60 weeks after conception. Individual predicted volumes, standardized to a 70-kg person, from the NONMEM post hoc  step are plotted against age. The solid line demonstrates the nonlinear relation between volume of distribution and age. The figure inset includes older children and shows the population estimates for apparent volume of distribution of 66.6 l/70 kg reached out of infancy. The x-axis (postconception age in weeks) of the inset figure uses a log scale. (B ) Individual predicted clearances, standardized to a 70-kg person, from the NONMEM post hoc  step are plotted against age up to 60 weeks after conception. The solid line demonstrates the nonlinear relation between clearance and age. The figure inset includes older children and shows the population estimates for clearance of 12.5 l · h⁻¹· 70 kg⁻¹reached out of infancy. The x-axis of the inset graph (postconception age in weeks) uses a log scale.