Cognitive bias A to Z

Lapses that come from divided attention at the moment of encoding or of acting, not from lost memories.

Responsibility spread so widely across an AI project that nobody feels answerable for its decisions.

Acting by default rather than waiting, because visible effort feels safer than doing nothing.

We explain our own behaviour by the situation and the behaviour of others by character.

We read our feeling about a thing as information about its risks and benefits.

The shortfall between understanding how AI systems work and how confidently people use them.

Systematic, repeatable unfairness produced by a system and its data rather than by a mind.

Avoiding options whose probabilities are unknown, in favour of options whose odds are stated.

The first number we are given pulls every later judgement towards it, even when it is irrelevant.

A single vivid case is treated as evidence of a general effect.

We attribute minds, intentions and feelings to things that have none.

Treating an idea as better because it is new.

Treating something likely, or merely possible, as though it were certain.

Concluding a claim is false because the argument offered for it was bad.

A word never presented is recalled as vividly as the studied words that all point to it.

Our tendency to focus on some elements of our environment while ignoring others.

Treating a claim as more valid because an authority figure made it.

Favouring the answers of an automated system even when we can see contradictory evidence.

We judge how likely something is by how easily an instance of it comes to mind.

The claim that correcting a false belief strengthens it, which has largely failed to replicate.

Adopting a behaviour or belief because many other people have.

We read generic descriptions that would fit almost anyone as precise portraits of ourselves.

Given both a statistical base rate and a specific description, we weight the description and neglect the rate.

We judge an argument valid when we agree with its conclusion.

A belief outlives the evidence that created it, even after that evidence is withdrawn.

Doing someone a favour makes us feel more positively toward them.

We recognise bias in other people and not in ourselves, because we judge ourselves from the inside.

Asked what follows logically, people answer from content, word order and familiarity instead.

Groups spend their time on trivial items and wave the consequential ones through.

Odd or incongruous material is recalled better than ordinary material, but only under narrow conditions.

A purchase that exhausts its budget is enjoyed less than the same purchase made with money to spare.

We satisfice rather than optimise, because our information and computing capacity are limited.

Bought as a bundle, items get used less than the same items bought one at a time.

Seeing or hearing the word bye is said to activate buy, and to raise willingness to spend.

We spend more freely when no physical money changes hands.

We rate an outcome likelier when it belongs to a large category than to a small one.

A face is rated slightly more attractive when seen in a group than when seen on its own.

Too many options degrade the decision, or prevent it being made at all.

We remember the option we chose as better than it was, and the ones we rejected as worse.

Random data contains streaks and gaps, and we read them as structure.

The discomfort of holding conflicting beliefs, and the reasoning we do to make it stop.

We stay with a course we chose, especially in public, even as the results come in bad.

A false account given sincerely, with no intention to deceive and usually no sense of doubt.

We search, read and remember evidence in ways that shield a hypothesis from rejection.

We test our favoured hypothesis directly and never run the test that would rule it out.

A conjunction is judged more probable than one of the things it is a conjunction of.

Given new evidence we move our beliefs in the right direction, but by too little.

We recall past attitudes and behaviour as closer to our present ones than they were.

Material is easier to retrieve in the setting where it was learned than in a different one.

Retracted information keeps shaping inferences after the person has accepted the retraction.

A thing looks better or worse depending on what we happened to see immediately before it.

Faces from our own racial group are recognised more accurately than faces from other groups.

An idea comes back as our own because we remember the idea but not where we got it.

Material we cannot recall is often still stored, and fails only because the right cue is missing.

Once we know something we cannot model a mind that does not, so we explain it badly.

The quality of our decisions falls as we make more of them.

Believing things were better before and are getting worse.

Adding a third, clearly inferior option changes which of the original two we choose.

We assign blame for a mishap in whatever way leaves us least likely to suffer one.

Steadily expanding what we let automated systems do, while oversight quietly thins.

We set our clearest and most detailed goals for the parts of life that matter least.

The same sum of money is easier to spend as small units than as one large one.

We sell what has gone up and hold what has gone down.

Differences that loom large side by side barely register once we live with the choice.

Lacking skill in an area also removes the means to see that we lack it.

How long an experience lasted barely enters our later judgement of how good or bad it was.

We rate an outcome more highly for having worked hard to get it.

We recall our own contribution more readily than anyone else, and claim a larger share of the result.

A solution that has worked before blocks us from seeing a better one that is available.

Underestimating how much a different mental state — ours or someone else’s — changes behaviour.

Owning something raises what we demand to give it up above what we would have paid for it.

We attribute other people’s motives to external rewards and our own to internal ones.

The unpleasantness attached to a memory fades faster than the pleasantness attached to one.

Overestimating how far other people share our beliefs, values and behaviours.

A whole event that never happened can be remembered, with detail and confidence, as if it had.

Whatever we are thinking about seems to matter far more to happiness than it does.

The same facts become more or less attractive depending on which of their features are highlighted.

After noticing something for the first time, we see it everywhere and take that for a real increase.

We cannot see an object as anything other than what it is normally used for.

Judging others’ behaviour, we overweight their personality and discount the situation they are in.

Believing that the outcome of a random event is influenced by the outcomes that came before it.

Material we produce ourselves is remembered better than the same material read.

We forget information we know we can look up again.

We read a group decision as the preference of every member, and one member as the whole group.

A group ends its discussion further out than its members started, and more confident about it.

A group converges on one view and its members quietly abandon the doubts they came in with.

A positive impression in one area colours our judgement of a person, brand or product in unrelated areas.

Confidence exceeds accuracy on hard question sets and falls short of it on easy ones.

Rules of thumb that make judgement fast and cheap, and sometimes systematically wrong.

Once we know the outcome, we misremember having expected it.

It always takes longer than you expect, even when you allow for it taking longer.

Believing that someone who has just succeeded is more likely to succeed again.

Humorous material is recalled better than neutral material, largely at the expense of the material around it.

We choose immediate rewards over later ones, even when the immediate reward is smaller.

We feel more, and give more, for one named person than for a large anonymous group.

We value what we built ourselves far above what the same thing is worth to anyone else.

We believe we know others better than they know us, and that our side sees theirs more clearly.

Believing we have more influence over events than we actually do.

We think we understand how things work in detail, until we try to explain one.

We credit whoever handed us an outcome for a satisfaction we produced ourselves.

We overestimate how visible our thoughts and feelings are to other people.

Overconfidence in our own interpretations and predictions from a coherent but weak set of data.

Improvement that did not occur is remembered, because the past self is reconstructed to flatter the present one.

Perceiving a relationship between two variables where none exists.

Most people place themselves above the median on most desirable traits, which cannot be true of most people.

Repetition makes a statement feel truer, whether or not it is true.

Overestimating how intense and how long-lasting our emotional reaction to a future event will be.

A reaction-time task whose scores are widely read as a measure of hidden prejudice.

Group-linked associations activate automatically, whether or not the person endorses them.

Giving preferential treatment to people who belong to the same group as us.

Attaching a reward to a behaviour, or a penalty to its absence, and expecting behaviour to follow.

Seeking more information even when no possible answer would change what we do.

Each person sensibly defers to those who spoke first, and the group ends up knowing less than its members.

How likely a sample result is gets judged without using how large the sample was.

Believing people get what they deserve, so what happened to someone tells us about them.

Longer gaps between repeated study of the same material produce better long-term retention.

Having mastered a method, we start finding problems everywhere that seem to call for it.

Judged on its own, the lesser option can beat the option that would beat it in a direct comparison.

When we retell a memory we drop the minor details and exaggerate the ones we think matter.

How material is encoded decides how well it is remembered: meaning beats repetition.

A long-disputed claim that the language we speak shapes what we notice and think.

The share of a list we recall falls as the list grows, even as the total recalled rises.

A result that looks significant may have arisen by chance, because so many hypotheses were tested.

A loss is felt about twice as strongly as an equivalent gain.

A capacity limit, not a bias: immediate memory holds a handful of chunks, and probably nearer four than seven.

Concluding that two things differ because someone knows them under different descriptions.

Retrieving some material actively suppresses related material that was not retrieved.

We label money by where it came from and what it is for, then treat the labels as real.

We come to like things simply because we have encountered them before.

Judging the validity of information by who is delivering it.

Information supplied after an event alters what a person remembers seeing.

The last few items in a list are recalled better when heard than when read.

We read money at its face value and forget what it will buy.

Our current mood makes material that matches it easier to recall than material that does not.

Having done something good makes us freer to do something questionable next.

We praise and blame people for outcomes they did not control, which philosophy calls moral luck.

A question containing a wrong but fitting term is answered rather than questioned.

An uncertain reward can motivate us more than a certain one of greater value.

The adage that anything that can go wrong will go wrong, sustained by selective memory.

We spread resources evenly across whatever set of categories happens to be put in front of us.

We expect other people to be more self-serving than they actually turn out to be.

Believing we see things as they are, so anyone who disagrees must be misinformed or biased.

Negative events and feelings affect us more than positive ones of equal size.

Under uncertainty, the probability is not weighted badly — it is not used at all.

We remember little of what happened in the moments just before our own turn to perform.

Social responsibility earns a firm goodwill that transfers to judgements of its products.

Underestimating the possibility of disaster and assuming life will continue as normal.

Reminiscing about the past makes money feel less important, and spending easier.

Ideas, tools and evidence from outside are rejected for being from outside.

Expectations held by a researcher change the behaviour of the people being observed.

A rule for choosing between explanations that fit equally, not a claim that the simple one is true.

We judge harm we caused by acting as worse than the same harm we allowed to happen.

We rate our own chances of good outcomes too high and of bad ones too low.

Which way a familiar object faces is remembered wrongly, confidently, after thousands of exposures.

Avoiding negative information, and avoiding feedback on our own performance.

We perceive less variety among members of other groups than among members of our own.

Judging a decision by how it turned out rather than by what was knowable when it was made.

Confidence in our judgements exceeds their accuracy, though how much depends heavily on how the questions were chosen.

A reward for something we already enjoy can replace the enjoyment as the reason for doing it.

Treating human-like chatbots as trusted social partners rather than tools.

Seeing a definite thing, most often a face, in material that contains nothing of the kind.

Being shown some of the items you are trying to recall makes the remaining ones harder to retrieve.

We judge an experience by its most intense moment and how it ended, not by its duration.

Safety regulation delivers less than promised because people take more risk once protected.

Overestimating the chance of bad outcomes and underestimating the chance of good ones.

Concepts studied as pictures are recalled and recognised better than the same concepts studied as words.

Improvement produced by the expectation of a treatment rather than by the treatment.

Underestimating how long a task will take, and what it will cost and risk.

Privately rejecting a norm while assuming that almost everyone else accepts it.

Pleasant material is processed, judged and recalled more readily than unpleasant material of the same intensity.

Older adults attend to and remember positive material more than negative, relative to younger adults.

After choosing, we upgrade what we bought and downgrade what we turned down.

An evaluation of a person that follows from the category they are assigned to.

Giving disproportionate weight to rewards that arrive sooner, even when a larger payoff is available later.

We remember what came first better than anything that follows, and judge the rest against it.

Exposure to one stimulus changes the response to a later one, with no awareness of the link.

An innovation is assumed to benefit everyone, and non-adoption is treated as a failure to be overcome.

Material that costs more effort to process is sometimes better retained, but only certain kinds of effort.

Overestimating how much our future selves will share our current beliefs, values and behaviour.

An outcome that is certain only if an earlier stage goes well is treated as certain outright.

We treat a category as having a hidden inner nature that explains what its members are like.

A threatened freedom is reasserted, and the blocked option becomes more attractive for being blocked.

Studies with positive results reach print; studies that found nothing stay in the drawer.

Expectations held by others can become self-fulfilling, though the classroom effect is far smaller than its fame suggests.

Discounting a proposal because of who made it, particularly an adversary.

We remember and weight what came last more heavily than what came earlier.

Making a decision in order not to regret the alternative later.

We judge probability by how closely a case resembles a mental prototype.

Organisations reallocate resources far less than their stated strategy implies.

Giving inaccurate or false answers to self-report questions in surveys and structured interviews.

Overestimating our ability to resist temptation — and therefore exposing ourselves to more of it.

Advocating the opposite of what you want, so the other person asserts their freedom by choosing it.

Statements that rhyme are judged more true than the same claims in prose.

People adjust how much risk they take to keep their felt level of risk roughly where it was.

We remember experiences more favourably than we experienced them, and the past more fondly than the present.

We attend to whatever stands out and discount whatever does not, regardless of importance.

We notice and retain what fits our commitments and let discrepant material pass unregistered.

Material judged against ourselves is remembered better than the same material processed for meaning alone.

We claim our successes as ours and push our failures onto circumstances.

The reflex rejection of new evidence because it contradicts established practice.

We remember the first and last items in a sequence and lose the middle.

Recalling items in their original order is a separate capacity from recalling the items themselves.

Overestimating another person’s sexual interest in oneself — predominantly in men.

We judge ourselves against the people around us, and resent those the comparison places above us.

People report the answer that looks good rather than the answer that is true.

Collectively held beliefs about which behaviour is appropriate in a given situation.

A memory error in which we cannot recall where a memory came from.

Repetitions spread over time are remembered far better than the same repetitions crammed together.

We think other people notice and remember our appearance and slips far more than they do.

We prefer things to stay as they are, and treat the default as the safe choice.

A category, once applied to a person, supplies expectations about what has not been observed.

We search where the data is easy to collect rather than where the answer is likely to be.

Naming the parts of a category raises its total judged probability above the whole.

A statement feels accurate because it means something to us, not because it fits.

One irrelevant spoken word at the end of a heard list destroys the recall advantage of its last items.

Accepting and acting on ideas suggested by others, without independent checking.

We keep going because of what we have already spent, not because continuing is worth it.

Mistaking a successful subgroup for the whole group, because the failures are invisible.

We mistake a selection criterion for an effect of the activity we admire.

People defend the existing social order even when it works against them.

We decide between two options on the first cue that tells them apart, and ignore the rest.

We misplace events in time: recent ones feel remote, and remote ones feel recent.

Retrieving material from memory improves later retention more than restudying it for the same time.

We think persuasive media affect other people more than they affect us, and we legislate on that belief.

We badly misjudge the time gained by going faster, especially when already going fast.

A word we cannot produce but can partly describe, felt as being just out of reach.

We see our own behaviour as varying with the situation and other people as acting from fixed traits.

Good acts by our group are credited to character and by other groups to circumstance, and bad acts reverse.

We treat whatever counts as one portion as the right amount to take.

An item that differs from a uniform set around it is remembered better than the rest.

A change must be a constant proportion of what is already there before we notice it at all.

A familiar route feels shorter than an unfamiliar one of the same length.

Preferring to eliminate one risk completely over a larger reduction in total risk.

We read a situation as a fixed pie, where any gain to one side must be a loss to the other.