The findings, to be published in the journal Psychological Science, demonstrate the power of what the researchers have termed "unit bias": the sense that a particular portion of food is appropriate. Unit bias provides the basis for understanding why portion size influences how much food you eat. Their work on how individuals decide what goes into a single serving of food offers further warning to the weight-conscious in the coming holiday season.

"In terms of food, unit bias applies to what people think is the appropriate amount to consume, and it shows why smaller portion sizes can be just as satisfying," said Andrew B. Geier, lead author and a graduate student in Penn's Department of Psychology. "A 12-ounce can of soda and a 24-ounce bottle are both seen as single units. But be careful, the 24-ounce bottle, though viewed as one unit, is actually more than two and a half servings of soda."

Unit bias can be seen in all types of consumption, whether it is how much food you take or how many times you ride the roller coaster. This bias, the researchers believe, is mostly derived from a culturally designated "proper" portion. It may also explain why portion size causes the French to eat much less than Americans.

"The French eat from smaller portion sizes, but small portion size is only a barrier if there is something keeping them from consuming more portions," Geier said. "This is where we believe unit bias comes into play; without it, people would just eat more units."

According to Geier, people see food in natural consumption units, whether that is a single wrapped candy or a plateful of food.

Geier and Penn psychology professor Paul Rozin designed their experiments to observe how people choose to act in the presence of unlimited free food in
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Contact: Greg Lester
glester@pobox.upenn.edu
215-573-6604
University of Pennsylvania
21-Nov-2005