Dr. Blanch-Payne wants to examine whether a prevention program can reduce peer bullying in school. She selects 7 classrooms. At the start of the school year, she randomly assigns five of the classes to the bullying prevention program, but not the other two classes. At the end of the year, Dr. Blanch-Payne compares the rate of peer bullying between those classes who received the prevention program and those classes who did not.