Figure 1.2 Design of Aerobic Exercise and Anxiety Experiment Participants are randomly assigned to groups in order to equalize participant characteristics across the groups. The placebo group controls for the placebo effect, and the control group provides a baseline level of anxiety reduction for participants who do not participate in the aerobic exercise program or receive a placebo. The level of anxiety reduction for each group is determined by comparing the measurements of the dependent variable (level of anxiety) before and after manipulating the independent variable (aerobic exercise).