A psychology graduate student conducted a study at the entrance to a football game at the university. The entrance was specifically for students who made the Dean's List for academic achievement during the previous semester. As they arrived, the graduate student asked half of the students to record their attendance on an attendance sheet. The remaining half were allowed to enter the game without recording their attendance. The graduate student told every student to take one soda and one hamburger from a concessions table sponsored by the Dean's Office. She then returned to the sign-in table out of sight of the concessions. This gave the students the opportunity to take additional food. The graduate student measured the percentage of students who took additional free food. Her hypothesis was that students would take more food when they were not asked to sign in. The results are shown in the graph below; assume all differences are significant.