Fig. 3. Example Bispectral Index trends for virtual patient 1 controlled by the proportional integral derivative (PID) controller (A ) and model-based controller (B ). Black line = target 70; light gray line = target 50; dark gray line = target 30. Stimulation events A –H  are described in the legend for figure 2. Tighter control was achieved with the model-based controller because Bispectral Index values were more frequently near their respective target levels.