Mental shortcuts that mislead
Your mind judges how likely something is by how easily examples come to mind and how typical it looks. Both shortcuts are quick, and both can steer you wrong.
PsychologyThink clearlyAbout 6 min: 3 reading, 3 practiceUpdated
Educational, not medical or mental-health advice.
- Explain the availability and representativeness shortcuts
- Spot when vivid or typical-looking examples are steering a judgement
- Ask the question that corrects each one
Builds toward: Think clearly. Catch common thinking errors in yourself and in other people's arguments, and make better calls when you can't be sure.
Think clearly: thinking errors and better decisions: lesson 1 of 7
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Pairs with Tversky and Kahneman (1974), "Judgment under uncertainty: Heuristics and biases"; OpenStax, Psychology 2e, section 7.3 "Problem Solving"
What it is
A heuristic is a mental shortcut: a quick rule of thumb that gives an answer without working it all out. Most of the time shortcuts serve you well. In 1974 the psychologists Amos Tversky and Daniel Kahneman showed that a few of them also lead to errors that are systematic: most people make them, in the same direction.
Availability. You judge how common or likely something is by how easily examples come to mind. Things you have seen recently, or that were vivid, frightening or in the news, come to mind easily, so they feel more common than they are.
Quick check
Tap an answer to check it.
After a week of news stories about a plane crash, Sam feels flying is more dangerous than driving. Which shortcut is at work?
- Representativeness is about resemblance, not how easily examples come to mind
Show answer
Availability: the vivid crash comes to mind easily, so it feels likely. A frightening, much-reported event is easy to recall, so it feels more common than it is.
Quick check
Tap an answer to check it.
A quiet man who loves poetry: is he more likely to be a librarian or a salesperson?
- Fitting the picture is representativeness; it ignores how many of each there are
Show answer
It depends: there are far more salespeople than librarians, so the numbers may still favour salesperson. Resemblance is only half the question. How common each job is matters too.
Why it matters
These shortcuts shape real decisions: what you fear, what you insure against, whom you trust.
Availability and risk. In a classic study (Lichtenstein and colleagues, 1978), people overestimated how many deaths come from dramatic causes such as tornadoes and accidents, and underestimated quiet, common ones such as diabetes and stroke. The researchers linked this to how much more the dramatic causes are reported, which makes examples come to mind more easily.
Representativeness and the "Linda" problem. Tversky and Kahneman (1983) described Linda: 31, outspoken, a philosophy graduate who cared about discrimination and social justice. Asked which was more likely, Linda is a bank teller or Linda is a bank teller and active in the feminist movement, most people picked the second. But two things can never both be true more often than one of them alone: every feminist bank teller is also a bank teller. The detailed story felt more typical of Linda, so it felt more likely. This error is called the conjunction fallacy.
Representativeness and chance. After five reds in a row on a roulette wheel, many people feel black is "due", because a mixed sequence looks more typical of chance. The wheel has no memory: each spin has the same odds. This is the gambler's fallacy.
Worked example
Your friend says: "Don't let the kids walk to school. Did you see that story about the child who was taken? It happens all the time."
Take the judgement apart with two questions:
- Why does this come to mind so easily? One terrible, widely shared story. That is availability: how easily you recall it says little about how often it happens.
- What do the numbers say? Look up how often it actually happens where you live, from an official source such as police or government statistics, and compare it with the everyday risks you already accept, such as road traffic.
The answer may still be "take care", but now it rests on how common the danger is, not on how memorable one story was.
Common mistake
Thinking you are immune once you know the names. Knowing about availability does not stop a vivid story from feeling convincing. The fix is a habit, not knowledge: when a judgement feels obvious, ask "How often does this really happen?" and "How many of each are there to begin with?", and then look it up.
Key terms
- heuristic
- a mental shortcut that gives a quick answer without working everything out
- availability
- judging how likely something is by how easily examples come to mind
- representativeness
- judging how likely something is by how much it resembles a typical case
- conjunction fallacy
- judging two things together as more likely than one of them alone
- gambler's fallacy
- believing a random outcome is "due" because it hasn't happened for a while
Practise the key terms
Tap a card to turn it over. 5 cards.
| Front | Back |
|---|---|
| heuristic | a mental shortcut that gives a quick answer without working everything out |
| availability | judging how likely something is by how easily examples come to mind |
| representativeness | judging how likely something is by how much it resembles a typical case |
| conjunction fallacy | judging two things together as more likely than one of them alone |
| gambler's fallacy | believing a random outcome is "due" because it hasn't happened for a while |
Practice
Sort it
Which group does this belong to?
"Burglaries must be rising: two neighbours were burgled this month."
Two recent, close-to-home cases are easy to recallShow answer
Availability. Two recent, close-to-home cases are easy to recall
"He wears glasses and reads a lot, so he's probably a professor."
He fits a picture, but there are far fewer professors than other jobsShow answer
Representativeness. He fits a picture, but there are far fewer professors than other jobs
"I won't swim in the sea after watching that shark film."
A vivid film makes the danger easy to imagineShow answer
Availability. A vivid film makes the danger easy to imagine
"Six heads in a row, so tails is due."
A mixed run looks more like chance, but each toss is independentShow answer
Representativeness. A mixed run looks more like chance, but each toss is independent
Quick quiz
Tap an answer to check it.
Which is more likely to be true of Linda?
- Two things together can never be more likely than one of them alone
Show answer
Linda is a bank teller. Every feminist bank teller is also a bank teller, so the single statement is always at least as likely.
Why did people in the 1978 study overestimate deaths from tornadoes?
- They are a rare cause; diseases such as diabetes and stroke kill far more people
Show answer
Dramatic deaths are reported more, so examples come to mind easily. Media coverage makes some events easy to recall, which inflates how common they feel.
A coin has landed heads five times in a row. What is the chance of heads next time?
- The coin has no memory of past tosses
- A fair coin doesn't get hot or cold
Show answer
Still one in two. Each toss of a fair coin is independent of the last.
What is the most useful question when a vivid story makes something feel common?
- Strong feelings are what availability produces
Show answer
How often does this actually happen?. Checking the real frequency corrects the pull of a memorable example.
In short
- Heuristics are mental shortcuts: usually helpful, sometimes systematically wrong.
- Availability: easy to recall feels common. Vivid, recent and much-reported events seem likelier than they are.
- Representativeness: typical-looking feels likely, so we forget how common each kind of case is.
- The conjunction fallacy (Linda) and the gambler's fallacy both come from judging by resemblance.
- The fix is a habit: ask how often it really happens, and how many of each there are.
Mastery check
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Check yourself
Answer in your head first, then open the answer. Nothing is saved.
What is the availability shortcut, in one sentence?
Show answer
Judging how likely or common something is by how easily examples come to mind.
Why is "Linda is a bank teller and a feminist" never more likely than "Linda is a bank teller"?
Show answer
Because every feminist bank teller is also a bank teller, so the combined statement can only be true in the same cases or fewer.
A shy, tidy man: is he more likely to be a librarian or a farmer? What should you ask before answering?
Show answer
How many librarians and how many farmers there are. Farmers may far outnumber librarians, so the numbers can outweigh the description.
Further reading
- Tversky, A., & Kahneman, D. (1974). Judgment under uncertainty: Heuristics and biases. Science, 185(4157), 1124–1131.
- Tversky, A., & Kahneman, D. (1983). Extensional versus intuitive reasoning: The conjunction fallacy in probability judgment. Psychological Review, 90(4), 293–315.
- Lichtenstein, S., Slovic, P., Fischhoff, B., Layman, M., & Combs, B. (1978). Judged frequency of lethal events. Journal of Experimental Psychology: Human Learning and Memory, 4(6), 551–578.
- OpenStax, Psychology 2e, section 7.3, free online.
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