Unit Bias

A study displayed a bowl of M&M’s containing a spoon, inviting individuals to scoop as many as they wanted.

Participants ate more candy when served with a large spoon than when served with a small spoon.

A quantity corresponding to one unit appears as the optimum quantity.

See the full study here :

Geier, A. B., Rozin, P., & Doros, G. (2006). Unit bias: A new heuristic that helps explain the effect of portion size on food intake. Psychological Science17(6), 521-525

Explanation of the Unit Bias

Want to know more about biases?

Decision Fatigue

Peak-End Rule

Functional Fixedness