Random Intercepts Random Intercepts & Slopes Time (months) Time (months)

FIGURE 2.2: Graphical representation of the random-intercepts (left panel), and the random-intercepts and random-slopes (right panel) model for the evolution of the square root CD4 cell count in time for the patients in the AIDS dataset. Solid lines represent the average longitudinal evolutions, and dashed lines the subject-specic evolutions.