Psychology and numbers

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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Psychological / Cognitive Biases in User Research

An old friend got in touch to ask about confirmation bias in user research and if I had any resources. I shared them with him and I’m sharing them with you.

What is confirmation bias?

Confirmation bias states that we seek out / prefer / are drawn to data that supports our point of view, theory or hypothesis and are reluctant / shy away from / dismiss data that doesn’t support our point of view.

A great primer
Confirmation Bias – It’s Not What We Think We Know That Counts | Interaction Design Foundation

Some real science on confirmation bias
Under what conditions does theory obstruct research progress? – Semantic Scholar

Examples of confirmation bias
Examples and Observations of a Confirmation Bias

Other cognitive biases in user research

I worked as series editor on a fantastic book about User Research last year, well worth a read to improve your research skills:

  • Researching UX: user research (Aspects of UX) by Emma Howell and James Lang. Amazon UK | Amazon USA
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To our Brain Everything is a Location: A Unified Theory of Neuroscience

I graduated from my Neuroscience BSc back in 1998. The big takeaway from my degree was that as Francis Crick put it back in 1979

There is no theoretical framework for neuroscience

No over-arching theory about we go from neurone to brain. From perception to thinking, deciding, diverting attention. No unified view on how we encode data in our brain. How when we see a coffee is coffee cup, we recognise a coffee cup, we know what to do with a coffee cup, we pick it up and we can predict what’s inside.

Fast forward almost 40 years and it looks like we finally have that theory.

A Framework for Intelligence and Cortical Function Based on Grid Cells in the Neocortex for a neuroscience paper is easy-ish to read and understand.

The theory is simple and elegant. The groups of cells in our neocortex (the big ‘human’ bit of the brain) share a structure with the cells in our hippocampus. The hippocampus has been long known to help us map our body relative to the space around us. Mapping where our hands and feet are and the movements they make.

These Grid Cells in the neocortex use this same spatial encoding to encode objects and concepts. We represent ideas, objects and UIs as objects in space. We are all spatial thinkers.

Grid cells in the neocortex suggest all knowledge is learned and stored in the context of locations and location spaces and that “thinking” is the movement though these location spaces.

Ground breaking stuff. Finally a unified theory of neuroscience.

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Sludge Detectives: The “Behavioural Economics Police” Take On Hotel Booking Sites 

Love this. The term Sludge is a great one.

Sludge highlights how companies and organizations can and are taking advantage of innate consumer traits and fallibilities, such as inertia and inattention, knowing that they can profit from consumers’ weaknesses and biases.

Regulators are realizing the need to act as a type of “behavioral economics police” to protect consumers from a deluge of sludge.

From: Sludge Detectives: The “BE Police” Take On Hotel Booking Sites – Behavioral Scientist

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Humans are Bad at Multitasking

Well of course we are. It’s never been about gender. People are just bad at multi-tasking but really at kidding ourselves we can multitask.

Source: Research: Women and Men Are Equally Bad at Multitasking

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The Amazing Psychology of Japanese Train Stations 

There are some great behavioural nudges at Japanese (busiest in the world!) railway stations.

Source: The Amazing Psychology of Japanese Train Stations – CityLab

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Middle name initials enhance evaluations of intellectual performance 

So now you know. Add that middle initial and look more clever…

Middle name initials often appear in formal contexts, especially when people refer to intellectual achievements. On the basis of this common link, the display of middle initials increases positive evaluations of people’s intellectual capacities and achievements. We document this effect in seven studies:

Source: The impact of middle names: Middle name initials enhance evaluations of intellectual performance – Tilburg – 2014 – European Journal of Social Psychology

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Body Language Lessons from a Poker Pro

If you’ve been to one of my workshops you’ll know my obsession with body language. Here are some great tips:

via Swiss Miss

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Specific parts of the brain do many things

A really interesting study looking at the different regions of the brain do many things, rather than the received wisdom that each brain region is specialised for one thing.

What Does Any Part of the Brain Do? – Neuroskeptic

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The Neuroscience of Changing Your Mind 

Great stuff. It explains why changing one’s mind is so hard.

Xu hopes these insights into how difficult it is for the brain to amend its plans—a task that only gets harder as we age and neural communication slows—can eventually help researchers devise ways to intervene and help us make faster, safer decisions.

Source: The Neuroscience of Changing Your Mind – Scientific American

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