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).