Fig. 6. The validation data set. A shows the relation between the measured Bispectral Index (BIS) and propofol plasma concentration (Cpprop). B shows BIS versus effect site concentration (Ceprop), based on ke0estimate by NONMEM. To visualize the source data and results for the fixed number model, we showed the measured BIS data ≥ 90 as black circles . The second part (the sigmoid Emaxmodel using BIS < 90) data are shown as straight lines. C shows the individual prediction error (PE) from the best fitting model (fixed ≥ 90, sigmoidal < 90, 10-s delay; including estimates of interindividual variability on ke0and Ce50).