Category
Cognitive biases
A cognitive bias is a systematic pattern in how people judge, decide or remember, a tendency to depart from what logic, probability or the available evidence would support, in a predictable direction. Random mistakes aren’t biases. A bias is the mistake that keeps pointing the same way.
Fallacies are properties of arguments. Biases are properties of people. You can find a fallacy in a written argument without knowing anything about its author; a bias is a claim about how human minds tend to work.
The best-known bias of all isn’t in the list below. Confirmation bias is an umbrella term for several distinct tendencies, in how people look for evidence, read it and remember it, and each of those has its own research record. No single replication status could describe them all, so it has its own page under Principles.
Entries (39)
- Actor–observer asymmetryLargely failed to replicateThe claim that people explain their own behavior by the situation but other people’s by their character, which a large meta-analysis did not support.
- Anchoring effectReplicates robustlyLetting a number you’ve just considered pull your estimate toward it, even when that number tells you little.
- Attraction effectContestedBeing drawn toward an option because a clearly worse version of it is also on offer, although that worse option says nothing new about your real choice.
- Availability heuristicReplicates robustlyJudging how common or likely something is by how easily examples of it come to mind.
- Backfire effectLargely failed to replicateThe claim that correcting a false belief makes people believe it more strongly, which large replications have rarely found.
- Base rate neglectContestedJudging how likely something is from the details of one case while giving too little weight to how common it is in the first place.
- Belief biasContestedJudging whether an argument is logically valid by whether you already believe its conclusion.
- Belief perseveranceReplicates robustlyKeeping a belief, at least in part, after the evidence it was based on has been shown to be false.
- Bias blind spotReplicates robustlySeeing biases at work in other people’s judgments more readily than in your own.
- Conjunction fallacyReplicates robustlyJudging that two things happening together is more likely than one of them happening on its own.
- Curse of knowledgeContestedFinding it hard to imagine not knowing something you know, so you overestimate how much others know or how easily they’ll understand you.
- Disconfirmation biasContestedChecking arguments against your view much harder than arguments for it, so the unwelcome ones reliably come out looking weaker.
- Dunning–Kruger effectContestedThe claim that people who are bad at something overestimate how good they are, because judging the skill takes the skill.
- Endowment effectContestedValuing something more just because it’s yours, so you’d demand more to give it up than you’d pay to get it.
- False consensus effectContestedOverestimating how many other people share your opinions, choices and habits.
- Framing effectReplicates robustlyMaking a different choice when the same facts are described differently, such as “90% succeed” versus “10% fail”.
- Fundamental attribution errorReplicates robustlyExplaining what someone did by the kind of person they are, while underweighting the situation that produced it.
- Gambler's fallacyReplicates robustlyExpecting a run of one outcome in a random process to make a different outcome more likely next, as if chance kept score.
- Halo effectReplicates robustlyLetting one overall impression of someone color your judgment of their unrelated traits.
- Hindsight biasReplicates robustlyBelieving, once you know how something turned out, that the outcome was more predictable than it really was.
- Hot hand fallacyContestedExpecting a run of successes to continue because the streak seems “hot”, more than the process behind it justifies.
- Illusion of controlContestedBelieving your actions influence an outcome that is really down to chance, or that you control events more than you do.
- Illusion of explanatory depthReplicates robustlyBelieving you understand how something works, such as a zipper or a toilet, in far more detail than you could actually explain.
- Illusory correlationReplicates robustlySeeing a link between two things that isn’t in the data, or seeing a weak link as a strong one.
- Illusory truth effectReplicates robustlyRating a statement as more likely true because you’ve encountered it before, even though hearing it again adds no evidence.
- In-group biasReplicates robustlyFavoring members of your own group over outsiders, in how you judge them and what you give them, even when the group is arbitrary.
- Loss aversionContestedWeighing a loss more heavily than a gain of the same size, so that a fair or even favorable bet feels like a bad deal.
- Moral licensingContestedThe claim that doing something good makes people feel entitled to something bad afterward, which large replications have mostly not found.
- Negativity biasContestedGiving bad events, feedback or information more weight than good ones of the same size.
- Outcome biasReplicates robustlyJudging whether a decision was good by how it happened to turn out, rather than by what was known and reasonable when it was made.
- OverconfidenceReplicates robustlyBeing more sure your judgments are right than your track record justifies, such as giving “90% sure” ranges that catch the truth far less often.
- Planning fallacyContestedForecasting how long a task will take, or what it will cost, from the plan for it rather than from how similar tasks actually went.
- Present biasContestedGiving extra weight to whatever is immediate, so that plans made for later are reversed when later becomes now.
- Regression fallacyContestedGiving the credit or blame for a change to something that happened in between, when an unusual result was simply returning toward average.
- Scope insensitivityContestedValuing a good outcome about the same whether it is small or many times larger, as if the number involved barely mattered.
- Self-serving biasReplicates robustlyCrediting your successes to yourself and blaming your failures on circumstances, luck or other people.
- Status quo biasContestedSticking with the current state of affairs, or a past choice, because it’s current, when you’d pick something else starting fresh.
- Sunk cost fallacyContestedSticking with something because of what you’ve already spent on it, when only what happens next can make it worth continuing.
- Unrealistic optimismContestedExpecting your own future to turn out better than the evidence supports, or better than other people’s.
Biases are empirical claims
Because a bias is a claim about human psychology, it is established by experiments, and experiments can be wrong. Several famous biases have not held up when other researchers tried to repeat the studies. Every bias on this site carries a replication status:
- Replicates robustly: found repeatedly, by independent researchers, with different methods.
- Contested: real disagreement about whether the effect exists, how big it is, or what causes it.
- Largely failed to replicate: careful attempts to repeat the key findings mostly haven’t found it.
Biases are often shortcuts
Many biases are side effects of mental shortcuts (heuristics) that work well most of the time. Judging quickly from limited information is usually useful, and the bias shows up where the shortcut breaks. Some researchers explain several biases through a single underlying habit, such as “what you see is all there is”.
Knowing about a bias doesn’t switch it off
Most biases operate without awareness, and learning the name of one does little to stop it. What helps more is changing the situation: collecting independent evidence, judging one thing at a time, or deciding what would count as evidence before looking.
Other categories: Formal fallacies · Informal fallacies · Research biases