The authors conducted experiments with offering free food in public areas, varying the size of the product unit and the size of the serving utensil. In one experiment, researchers observed a mixing bowl of M&M's in the lobby of an apartment building, setting the serving spoon size at variance. The results demonstrate an identifiable unit bias, as passersby tended to take a single unit or spoonful of food without consideration for its size or quantity. As tests were conducted both within eyesight of others and in a more discreet location, the bias in favor of consuming a single unit cannot be attributed solely to the avoidance of perceptible gluttony.
"It is more than just people being afraid of appearing greedy," state the authors. "We have a culturally enforced 'consumption norm,' which promotes both the tendency to complete eating a unit and the idea that a single unit is the proper amount to eat." The concept of unit bias helps explain how environmental differences in portions and package sizes impact overall consumption and may provide a foundation for a better understanding of the psychology of obesity.