Cognitive biases field guide

Every bias named in a public catalogue, three books and two standing collations: 234 entries, eighteen families, read for what each one means for learning.

A bias is not a fault in the machine. It is the machine working as designed, on the wrong problem.

Every entry here is a rule that earns its keep most of the time and fails in a describable set of cases. Which is why the useful question is never whether you are biased.

Six collations, one structure

Six sources set the scope: a public catalogue, three books, a widely used cheat sheet and the encyclopaedia list that cheat sheet regroups. Between them they name 234 distinct biases, effects and fallacies, and every one has an entry here. They are a starting point for the collation rather than the content of it: the writing, the structure, the counters and everything in the learning and edtech sections are this guide’s own.

Where the weight sits

Memory and self-assessment carry a quarter of the guide between them — a fact about the research literature rather than about the mind.

Where the scope came from

These six set the scope. Between them they name 234 distinct biases, effects and fallacies, and every one has an entry here.

A heuristic and a bias are the same rule, judged in different places

FIG 02 — FIVE STAGES OF A DECISION, EACH WITH A POINT WHERE BIAS ENTERS

Seven sections, the same seven every time

The structure is fixed across all 234 entries so that the guide can be read in two directions: down a family, comparing mechanisms, or across the collection, comparing a single field — every counter-move, or every origin, or every edtech implication.

Knowing about a bias is the weakest move available against it

Almost every counter-move in this guide changes a condition. The ones that ask you to try harder are the ones the research is least able to support.

Input

What reaches us, what we keep of it, and what the keeping does to it.

What we notice

Nothing can bias a judgement it never reached. The first filter is attention, and it is not neutral.

Attentional bias

Our state and our preoccupations decide which cues reach us, and the rest go unseen.

Salience bias

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

Identifiable victim effect

One named person with a face draws more sympathy and money than thousands counted in a statistic.

Bikeshedding

Discussion time runs inverse to importance: groups debate the trivial and wave the consequential through.

Priming

What we have just met shapes how we read what comes next, and we never notice the hand-off.

Mere exposure effect

Liking grows with repeated contact, even when nothing about the thing has changed but its familiarity.

Context effect

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

Frequency illusion

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

Mood congruence

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

Selective perception

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

Focusing illusion

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

Streetlight effect

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

The shortcuts themselves

Before the individual biases, the machinery that produces them: a mind spending a finite budget.

Heuristics

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

Bounded rationality

With limited time, knowledge and processing power, we take the first option that is good enough.

Availability heuristic

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

Affect heuristic

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

Decision fatigue

Each choice wears judgement down, and later ones drift towards the easy default.

Choice overload

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

What we keep

The largest section in the guide, and the one with the most to give back: these are the mechanics of how practice actually works.

Serial position effect

In any list, recall favours the two ends, and the items in the middle are the ones that go missing.

Primacy effect

What arrives first gets the firmest hold, and frames how everything after it is read.

Recency effect

The latest item in a sequence is the freshest in memory and carries more than its share of the verdict.

Lag effect

Within spaced study, the wider the gap between repetitions, the longer the material lasts, up to a point.

Spacing effect

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

Levels of processing effect

Working with what material means makes it stick far better than handling its surface or repeating it.

Google effect

When a search can find it, we keep the location and let the answer go.

Bizarreness effect

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

Generation effect

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

Humour effect

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

Memory inhibition

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

Modality effect

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

Next-in-line effect

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

Part-set cuing effect

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

Picture superiority effect

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

Self-reference effect

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

Serial recall effect

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

Testing effect

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

Tip of the tongue

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

Von Restorff effect

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

Cue-dependent forgetting

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

List-length effect

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

Suffix effect

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

Absent-mindedness

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

Processing difficulty effect

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

The magic number seven

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

What the keeping does to it

Memory is reconstruction, not retrieval. Every act of remembering edits the thing remembered.

Peak-end rule

We store an experience as its sharpest moment plus its ending, and its length barely registers.

Levelling and sharpening

Each retelling of a memory trims the minor details and inflates the few that carry the point.

Source confusion

We keep a memory but lose track of its source, and fill the gap with a guess.

Suggestibility

Ideas offered by someone else are taken up as our own and acted on without a check.

Telescoping effect

We misdate events, most often by pulling them closer to the present than they really were.

Rosy retrospection

Looking back, an experience seems better than it felt at the time, and the past outshines the present.

Associative memory illusions

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

Consistency bias

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

Fading affect bias

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

False memory

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

Illusions of change

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

Implicit stereotype

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

Misinformation effect

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

Moses illusion

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

Orientation illusions in memory

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

Cryptomnesia

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

Duration neglect

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

Confabulation

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

Inference

Reading the odds, holding a belief, and judging an argument.

What the odds are

The mind is a pattern-finder in a world that generates patterns by chance.

Base rate fallacy

A vivid detail about one case drowns out the plain figure for how common such cases are.

Representativeness heuristic

How much a case looks the part stands in for how likely it actually is.

Gambler’s fallacy

We expect chance to even itself out, so after a run of one outcome the other feels overdue.

Hot hand fallacy

After a run of successes we expect another, though the evidence for real streaks is mixed.

Survivorship bias

We draw lessons from the winners still in view and forget the failures that dropped out of it.

Category size bias

An outcome feels likelier when it sits in a big group, though the size of the group says nothing about its odds.

Illusory correlation

We see two things moving together when, counted properly, they have nothing to do with each other.

Illusion of validity

Evidence that hangs together feels predictive, so we trust forecasts that weak data cannot support.

Illusion of control

We credit ourselves with steering outcomes that are really down to chance or to other people.

Clustering illusion

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

Conjunction fallacy

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

Insensitivity to sample size

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

Neglect of probability

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

Pseudocertainty effect

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

Subadditivity effect

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

Pareidolia

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

What we already think

A belief is not a hypothesis held loosely. It is a position defended, and the defence is largely invisible from inside.

Confirmation bias

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

Belief perseverance

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

Cognitive dissonance

When what we did clashes with what we believe, we ease the tension by bending the belief.

Illusory truth effect

Each repeat of a claim makes it more believable, whether the claim is accurate or not.

Naive realism

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

Barnum effect

A vague profile that would suit nearly anybody reads to us like a sharp likeness of ourselves.

Just-world hypothesis

Assuming the world settles its accounts, so that a person’s misfortune is read as something they earned.

Declinism

The sense that things are sliding, drawn from a tidied past and a noisy present.

Backfire effect

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

Choice-supportive bias

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

Congruence bias

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

Semmelweis reflex

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

Subjective validation

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

System justification

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

Continued influence effect

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

Conservatism in belief revision

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

Naive cynicism

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

Judging the argument itself

Eleven entries that are not all cognitive biases. Some are rules of argument, some are formal errors, and two are folk maxims that survive on selective memory.

Anecdotal evidence

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

Appeal to novelty

FIG 99 — BOTH PREMISES ARE TRUE AND NEITHER IS ABOUT LEARNING

Appeal to probability

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

Argument from fallacy

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

Belief bias

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

Biases in deductive reasoning

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

Information bias

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

Masked-man fallacy

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

Murphy’s law

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

Occam’s razor

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

Rhyme-as-reason effect

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

The social lens

Judging ourselves, judging other people, and moving with the crowd.

What we think we know

The one estimate we can never check against an outside source is the estimate of ourselves.

Dunning–Kruger effect

The skill to do a task is the skill to judge it, so the least able overrate themselves most.

Hard–easy effect

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

Illusion of explanatory depth

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

Illusion of transparency

Our nerves and intentions feel written on our faces, but other people read far less of them than we assume.

Spotlight effect

We feel watched and remembered, while most people barely registered the shirt or the stumble.

Self-serving bias

Wins get filed under our own ability and losses under bad luck, which leaves nothing to learn from.

Hindsight bias

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

Outcome bias

We grade a choice by the result it happened to get, not by the case that could be made for it at the time.

Optimism bias

We expect life to go better for us than for the people around us, and plan on that basis.

Pessimism bias

We expect the bad version of events, for ourselves or for the world, more often than the record supports.

Bias blind spot

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

Defensive attribution

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

Egocentric bias

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

Illusory superiority

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

Moral luck

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

Overconfidence effect

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

Pollyanna principle

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

Positivity effect

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

Third-person effect

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

Illusion of external agency

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

What we read into others

We explain our own behaviour by circumstance and everyone else’s by character — though even that asymmetry is smaller than its reputation.

Fundamental attribution error

We read other people’s actions as proof of character and overlook the pressures they were acting under.

Halo effect

One good quality spills over, so whoever impresses in one way gets rated well in every other.

Authority bias

A claim gains weight from the rank of whoever made it, whatever the claim itself is worth.

Messenger effect

We decide whether to believe something by sizing up the person who says it.

Pygmalion effect

A teacher’s expectation can shape the pupil it describes, though the classroom effect is far smaller than its fame suggests.

Extrinsic incentive bias

We assume other people are in it for pay and security, while we are in it for the interest.

Sexual overperception bias

Reading friendliness as sexual interest, a pattern reported mainly in men and now disputed.

False consensus effect

We take our own view for the common one and expect more agreement than we will find.

Cheerleader effect

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

Cross-race effect

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

Curse of knowledge

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

Group attribution error

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

Illusion of asymmetric insight

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

Out-group homogeneity

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

Trait ascription bias

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

Ultimate attribution error

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

Actor–observer bias

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

Psychological essentialism

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

Stereotyping

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

Prejudice

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

What everyone else is doing

A group is not a set of opinions. It is a set of guesses about the other opinions.

Bandwagon effect

The more people we see doing something, the readier we are to do it too, whatever its merits.

Social norms

The shared, mostly unwritten rules about what people here do and what they ought to do.

Pluralistic ignorance

Each person doubts the rule in private and stays quiet, sure that everyone else believes in it.

In-group bias

We favour people who share our label, even when the label was handed out at random.

Reactive devaluation

An offer loses value in our eyes the moment we learn the other side made it.

Benjamin Franklin effect

Helping someone raises our opinion of them, even when we disliked them before.

Noble edge effect

A company’s good deeds make its products seem better, even on qualities the good deeds cannot touch.

Group polarisation

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

Groupthink

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

Information cascades

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

Reverse psychology

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

Social comparison bias

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

Value

What a thing is worth, and what a loss is worth avoiding.

How the question is put

The same options, arranged differently, produce different choices from the same person.

Framing effect

Describe the same facts as a gain or as a loss and people choose differently, though nothing else has changed.

Anchoring bias

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

Decoy effect

An option nobody would pick can still steer the choice between the two that matter.

Distinction bias

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

Less-is-better effect

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

Naive allocation

Given several options at once, we split evenly between them, so whoever draws the categories sets the shares.

Bye-now effect

A claimed priming effect in which the sound of bye calls up buy and nudges spending upward.

Incentivization

Using rewards and penalties to steer behaviour, on the assumption that people will do what pays.

Overjustification effect

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

Contrast effect

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

Denomination effect

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

Weber–Fechner law

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

Unit bias

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

Linguistic relativity

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

What a thing is worth

Ten entries. Value tracks ownership, effort, the account the money came from, how much of that account is left, and how visibly the payment hurts.

Endowment effect

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

IKEA effect

Things we assembled ourselves seem worth far more to us than they are to anyone else.

Mental accounting

Money gets sorted into pots by source and purpose, and each pot is spent by its own rules, though a pound is a pound.

Cashless effect

Card and phone payments hurt less than handing over cash, so we spend more.

Bottom-dollar effect

Whatever we buy with the last of a budget gets blamed for the pinch, and is enjoyed less for it.

Bundling bias

Pay for things as a package and we use fewer of them, because no single item carries a price to justify.

Disposition effect

We cash in winners early and hold on to losers, waiting to get back to even.

Nostalgia effect

A warm memory of the past loosens our grip on money, making us readier to spend it and give it away.

Effort justification

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

Money illusion

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

Post-purchase rationalisation

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

What we stand to lose

A loss is felt more keenly than the equivalent gain — though how much more, and how generally, is now disputed.

Loss aversion

Losses sting more than equal gains please, by a disputed factor of about two.

Negativity bias

Bad things register louder and stay longer than good things of matching size.

Zero-risk bias

Taking one hazard to zero feels worth more than a bigger cut in overall harm spread across several.

Ambiguity effect

Offered a known gamble and an unknown one, we take the known, even when the unknown may well be the better bet.

Regret aversion

We choose so as to avoid kicking ourselves later, rather than for the best expected result.

Ostrich effect

When the news is likely to be bad, we leave it unopened, including news about how we ourselves are doing.

Normalcy bias

Because disaster has never happened to us, we treat it as something that will not, and react late when it does.

Motivating uncertainty effect

Not knowing what we will win can make us try harder than knowing we will win more.

Peltzman effect

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

Risk compensation

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

Zero-sum thinking

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

Action

The future self, the sunk past, and the tools already in our hands.

Who we will be later

We forecast the circumstances of our future selves reasonably well, and their feelings not at all.

Hyperbolic discounting

A short wait cuts a reward’s value steeply, so smaller-sooner wins until both options are far away.

Present bias

Anything we get now counts for extra, simply because it is now, against anything that comes later.

Projection bias

We assume the tastes and wants we have today will still be ours later, and choose for a future self who does not exist.

Empathy gap

From a calm state we badly misjudge how hunger, fear or craving will steer what we, or others, actually do.

Impact bias

We expect good and bad news to hit harder and linger longer than it does once it arrives.

Planning fallacy

Plans built from the inside run late and over budget, because the forecast ignores how similar projects went.

Restraint bias

Confident of our self-control, we walk into more temptation, and the extra exposure is what defeats us.

Time-saving bias

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

Well-travelled road effect

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

Hofstadter’s law

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

Doing and not doing

Two opposite failures sit side by side here: acting because acting looks like competence, and not acting because the default asks nothing.

Action bias

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

Status quo bias

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

Sunk cost fallacy

Money, time or effort already gone keeps us investing in a course that no longer pays its way.

Commitment bias

Having backed a course, and been seen to back it, we defend it harder as the bad results arrive.

Omission bias

Harm done by doing something feels worse to us than the same harm let happen by doing nothing.

Resource inertia

Organisations reallocate resources far less than their stated strategy implies.

Psychological reactance

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

Moral licensing

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

Delmore effect

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

The tools already in hand

Expertise is a set of solutions that worked before. That is its value and its failure mode.

Einstellung effect

The method that worked last time comes to mind first and stops us looking for a better one.

Functional fixedness

An object’s usual job hides its other uses, so the tool we need sits unseen in front of us.

Law of the instrument

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

Take-the-best heuristic

Choosing between two options, we check cues in order of past usefulness and stop at the first that separates them.

Not invented here

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

Pro-innovation bias

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

The machine and the method

Bias where the decision is delegated, and bias built into the measuring.

When the decision is delegated

Six entries, five of which The Decision Lab added as the machine entered the loop. They are the newest material in the guide and the least settled.

Automation bias

The machine’s answer wins over our own checks, and we stop looking at the evidence it was meant to summarise.

AI literacy gap

Confidence in using AI tools runs ahead of the understanding needed to judge what they produce.

Delegation creep

Each successful handover to an automated system invites the next, and the human checks thin out along the way.

Parasocial trust in AI

A chatbot that talks like a friend gets trusted like one, though it is a product with someone else’s goals.

Accountability diffusion in AI

When a decision passes through many hands and a model, no single person feels they made it.

Algorithmic bias

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

Anthropomorphism

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

Bias in the instrument

The last four are not biases of the decision-maker. They are biases of the method used to study everyone else.

Observer expectancy effect

What the researcher hopes to find leaks into how participants behave and how their behaviour gets recorded.

Response bias

Answers to surveys and interviews drift from the truth in predictable directions, whatever the respondent intends.

Look-elsewhere effect

Search enough places and something will cross the line by chance, so a single hit means little on its own.

Placebo effect

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

Publication bias

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

Social desirability bias

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

The Implicit Association Test

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

Swimmer’s body illusion

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

One catalogue, three books, two lists

Written by geraldajam.com, with six sources consulted along the way: The Decision Lab’s bias catalogue, three books and two standing lists. All six are credited in the reference list, with thanks. The writing is this guide’s own.

Every entry in this guide is indexed, with its definition, at https://www.geraldajam.com/library/glossary/field-guides/cognitive-bias-field-guide.