Unit bias is the tendency to treat a standard or default unit of something, such as a food serving size, as the appropriate amount to consume, leading a person to consume the whole unit even when it is more than they actually want or need. The psychologists Andrew Geier, Paul Rozin, and Gheorghe Doros documented the effect in a 2006 study, showing that people ate far greater amounts of Tootsie Rolls and pretzels when offered a larger unit size than a smaller one, and ate substantially more M&Ms when the candies were served with a larger spoon than a smaller one, in both cases with no limit on how many units or spoonfuls they could take. The finding helps explain why smaller portion sizes are often effective at reducing consumption: assuming a unit is not so small as to be trivial, such as a single grain of rice, finishing one unit appears to inhibit a person's impulse to keep eating.
Facts
Core ClaimA standard suggested amount of consumption, such as a food serving size, is treated as the appropriate amount, so a person tends to consume the whole unit even when it is more than they want or need. 1 Sources
1. List of cognitive biases, Wikipedia
Estimation, Baseline subsection, Unit bias entryQuote, Estimation, Baseline subsection, Unit bias entry
Unit bias: The standard suggested amount of consumption (e.g., food serving size) is perceived to be appropriate, and a person would consume it all even if it is too much for this particular person.
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