Figure 3.

Basic Scheme of the Main Principles of the Mixed-Effects Modeling Approach, the Gold-Standard Methodology in Pharmacometrics.

Fixed effects represent the parameter values that characterize the mean description of the population and random effects handle the unexplained variability of the model. This methodology describes not only the mean/typical behavior of the population, but also the individual profiles of each patient. Interindividual variability describes the difference between the population and individual profiles, whereas residual variability accounts for the differences between the individual predictions and the measured observations.