The Cognitive Bias Library

The interactive guide to cognitive biases — a Decision-DNA test, a daily spot-the-bias puzzle, and deep, research-grounded pages on 58 biases.

Decision Making

• Anchoring Bias — The tendency to rely too heavily on the first piece of information offered (the 'anchor') when making decisions.
• Sunk Cost Fallacy — The phenomenon where a person is reluctant to abandon a strategy or course of action because they have invested heavily in it, even when it is clear that abandonment would be more beneficial.
• Framing Effect — The bias whereby people decide on options based on whether the options are presented with positive or negative connotations; e.g. as a loss or as a gain.
• Zero-Risk Bias — A tendency to prefer the complete elimination of a risk in a sub-part of a problem even when the overall risk reduction is smaller.
• Decoy Effect — The phenomenon where consumers will tend to have a specific change in preference between two options when also presented with a third option that is asymmetrically dominated.
• Endowment Effect — The tendency for people to ascribe more value to things merely because they own them.
• Hyperbolic Discounting — The tendency for people to increasingly choose a smaller-sooner reward over a larger-later reward as the delay occurs sooner rather than later.
• IKEA Effect — A cognitive bias in which consumers place a disproportionately high value on products they partially created.
• Status Quo Bias — A preference for the current state of affairs. The current baseline (or status quo) is taken as a reference point, and any change from that baseline is perceived as a loss.
• Paradox of Choice — The observation that having many options to choose from, rather than making people happy and ensuring they get what they want, can cause them stress and problematize decision-making.
• Planning Fallacy — The tendency to overestimate the time, costs, and risks of future actions and at the same time overestimate the benefits of the same actions.
• Choice-Supportive Bias — The tendency to retroactively ascribe positive attributes to an option one has selected and/or demote the forgone options.
• Information Bias — The tendency to seek information even when it cannot affect action.
• Ambiguity Effect — The tendency to avoid options for which missing information makes the probability seem 'unknown'.
• Bike-Shedding Effect — The tendency to give disproportionate weight to trivial issues. Also known as Parkinson's Law of Triviality.
• Unit Bias — The tendency to want to complete a unit of a given item or task.
• Loss Aversion — The tendency to prefer avoiding losses to acquiring equivalent gains.

Probability & Belief

• Confirmation Bias — The tendency to search for, interpret, favor, and recall information in a way that confirms or supports one's prior beliefs or values.
• Availability Heuristic — The tendency to overestimate the likelihood of events with greater 'availability' in memory, which can be influenced by how recent, unusual, or emotionally charged they may be.
• Survivorship Bias — The logical error of concentrating on the people or things that made it past some selection process and overlooking those that did not, typically because of their lack of visibility.
• Gambler's Fallacy — The mistaken belief that, if something happens more frequently than normal during a given period, it will happen less frequently in the future.
• Base Rate Fallacy — If presented with related base rate information (i.e. generic, general information) and specific information (information only pertaining to a certain case), the mind tends to ignore the former and focus on the latter.
• Optimism Bias — The tendency to overestimate the likelihood of positive events and underestimate the likelihood of negative events happening to oneself.
• Ostrich Effect — The tendency to avoid dangerous or negative information. We bury our heads in the sand.
• Negativity Bias — The notion that, even of equal intensity, things of a more negative nature (e.g. unpleasant thoughts, emotions, or social interactions) have a greater effect on one's psychological state than neutral or positive things.
• Clustering Illusion — The tendency to erroneously consider the inevitable 'streaks' or 'clusters' arising in small samples from random distributions to be non-random.
• Conjunction Fallacy — The fallacy that occurs when it is assumed that specific conditions are more probable than a single general one.
• Barnum Effect — The tendency to accept certain information as true, such as character assessments or horoscopes, even when the information is so vague as to be worthless.
• Illusion of Control — The tendency for people to overestimate their ability to control events.
• Placebo Effect — A beneficial effect produced by a placebo drug or treatment, which cannot be attributed to the properties of the placebo itself, and must therefore be due to the patient's belief in that treatment.
• Belief Bias — The tendency to judge the strength of arguments based on the plausibility of their conclusion rather than how strongly they support that conclusion.
• Frequency Illusion — The phenomenon where the thing you just learned suddenly appears everywhere. Also known as the Baader-Meinhof phenomenon.

Social

• Dunning-Kruger Effect — A cognitive bias stating that people with low ability at a task overestimate their ability.
• Halo Effect — The tendency for positive impressions of a person, company, brand, or product in one area to positively influence one's opinion or feelings in other areas.
• Bandwagon Effect — The tendency to do (or believe) things because many other people do (or believe) the same.
• Fundamental Attribution Error — The tendency for people to under-emphasize situational explanations for an individual's observed behavior while over-emphasizing dispositional and personality-based explanations.
• Authority Bias — The tendency to attribute greater accuracy to the opinion of an authority figure (unrelated to its content) and be more influenced by that opinion.
• Groupthink — A psychological phenomenon that occurs within a group of people in which the desire for harmony or conformity in the group results in an irrational or dysfunctional decision-making outcome.
• False Consensus Effect — A cognitive bias whereby a person tends to overestimate the extent to which their opinions, beliefs, preferences, values, and habits are normal and typical of those of others.
• In-Group Bias — The tendency to give preferential treatment to others they perceive to be members of their own group.
• Spotlight Effect — The phenomenon in which people tend to believe they are being noticed more than they really are.
• Ben Franklin Effect — A person who has performed a favor for someone is more likely to do another favor for that person than they would be if they had received a favor from that person.
• Bystander Effect — The phenomenon where individuals are less likely to offer help to a victim when other people are present.
• Curse of Knowledge — A cognitive bias that occurs when an individual, communicating with other individuals, unknowingly assumes that the others have the background to understand.
• Self-Serving Bias — The tendency to attribute positive events to one's own character but attribute negative events to external factors.
• Just-World Hypothesis — The cognitive bias to assume that actions will have morally fair and fitting consequences; that 'you get what you deserve'.
• Identifiable Victim Effect — The tendency to offer greater aid when a specific, identifiable person ('victim') is observed under hardship, as compared to a large, vaguely defined group with the same need.

Memory

• Hindsight Bias — The common tendency for people to perceive events that have already occurred as having been more predictable than they actually were.
• Peak-End Rule — People judge an experience largely based on how they felt at its peak (i.e., its most intense point) and at its end, rather than based on the total sum or average of every moment of the experience.
• Google Effect (Digital Amnesia) — The tendency to forget information that can be found readily online by using Internet search engines.
• Misinformation Effect — The impairment in memory for the past that arises after exposure to misleading information.
• Zeigarnik Effect — The tendency to remember uncompleted or interrupted tasks better than completed ones.
• Recency Bias — The tendency to weigh the latest information more heavily than older data.
• Primacy Effect — The tendency to recall the first items in a list better than items in the middle.
• Rosy Retrospection — The psychological phenomenon of people sometimes judging the past disproportionately more positively than they judge the present.
• Cryptomnesia — Occurs when a forgotten memory returns without it being recognized as such by the subject, who believes it is something new and original.
• Context-Dependent Memory — The improved recall of specific information when the context present at encoding and retrieval are the same.
• Spacing Effect — The phenomenon whereby learning is greater when studying is spread out over time, as opposed to studying the same amount of content in a single session.