Psychology and numbers

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I get asked a lot about numbers and psychology. Here are some common questions and the answers I give.

Q: Are odd or even numbers more attractive?

Humans “prefer” round numbers.


  • Individuals tend to recall odd-ending prices less accurately than even-ending prices
  • Expressing a price as odd-ending increases the likelihood that it will be underestimated when recalled
  • People prefer to ignore the last available digit for conservation of memory
  • Americans cluster their tips around multiples of $5.
  • Preference for round prices is so strong that restaurant dinners will calculate an exact tip amount to arrive at a round check total.
  • Direct evidence that investors prefer round numbers when buying stocks
  • Stock prices cluster on round fractions

Source: Aesthetic preference for even or odd numbers

Not as simple as that of course:

  • Prices ending in “9” were more likely to find buyers, relative to the prices ending in “4”

Source: Effects of $9 Price Endings on Retail Sales: Evidence from Field Experiments

Q: What is the right number of items to put in a list / navigation menu / widget?

The psychology of lists, how many items is the best. Spoiler, it’s multiples of 10.
Power of Ten: The Weird Psychology of Rankings

I bust the myth of the magic number 7 +/- 2:
Miller’s number 7 ± 2: Psychology Myth Busting #2 – Joe Leech @mrjoe

The magic number when it comes to items in our heads all at once might be 4: (academic paper)
The magical number 4 in short-term memory: a reconsideration of mental storage capacity

Hick’s Law describes the time it takes for a person to make design is directly related to the number of options they have to choose from. Less options. Faster choice.

Hicks Law

Hick’s law

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