The unit bias

Nominal variables matter, even when we are deciding how much to eat on our plates:

To test [the unit bias], the researchers left a bowl of M&M sweets in the hallway of an apartment building with a sign that read “Eat Your Fill: please use the spoon to serve yourself”. Some days they left a tablespoon-sized scoop, other days they left a quartercup scoop that was four times as big. Passers-by could obviously help themselves to as little or as much as they wanted regardless of which spoon was provided, but on average, 1.67 times more M&M’s were taken on the days the big scoop was left compared with the tablespoon-sized scoop.

In another experiment, the researchers found that, measured by weight, significantly more pretzels were taken by passers-by when a complimentary bowl of 60 whole pretzels was left in an apartment building, compared with when a bowl of 120 half-pretzels was left. And it was a similar story when either a bowl of 80 small Tootsie rolls (an American snack bar) or a bowl of 20 large Tootsie rolls was left in an office building.

In other words, throughout the study, people took more food when the unit on offer was larger. “Consumption norms promote both the tendency to complete eating a unit and the idea that a single unit is the proper portion”, the researchers said.

Here is further information.  There is a lesson for macroeconomics in here, somewhere.