What Are Cognitive Biases?

Cognitive biases are systematic errors in thinking or patterns of deviation in judgment that occur in specific situations. The existence of most cognitive biases has been demonstrated in psychological experiments. Cognitive biases are examples of mental behaviors that have evolved over time. Some serve adaptive functions, helping us act more efficiently or make quicker decisions. Others arise from a lack of relevant thinking skills or from the inappropriate application of skills that were adaptive in other contexts.

Decision-Making and Behavioral Biases

• Bandwagon Effect – The tendency to do (or believe) things because many other people do (or believe) the same. Related to groupthink, herd behavior, and manias.
• Anecdotal Fallacy – Ignoring available statistical data in favor of personal stories or isolated examples.
• Bias Blind Spot – The tendency not to compensate for one’s own cognitive biases.
• Choice-Supportive Bias – Remembering one’s choices as better than they actually were.
• Confirmation Bias – The tendency to search for or interpret information in a way that confirms pre-existing beliefs.
• Congruence Bias – Testing hypotheses exclusively through direct testing, rather than considering alternative hypotheses.
• Contrast Effect – The enhancement or diminishment of a perception when compared with a recently observed contrasting object. For example, the death of one person may seem insignificant compared to the death of millions.
• Professional Deformation – Viewing things strictly through the lens of one’s profession, ignoring broader perspectives.
• Distinction Bias – Perceiving two options as more different when evaluated simultaneously than when evaluated separately.
• Endowment Effect – People often want to sell an object for much more than they would pay to acquire it.
• Aversion to Extreme Solutions – The tendency to avoid extreme decisions, opting for intermediate choices.
• Focusing Effect – Errors in prediction that occur when people place too much emphasis on one aspect of an event, leading to mistakes in forecasting future outcomes.
• Narrow Framing – Using an overly narrow approach or description of a situation or problem.
• Framing Effect – Drawing different conclusions depending on how data is presented.
• Hyperbolic Discounting – The tendency to prefer smaller, sooner rewards over larger, later ones, especially as both rewards get closer in time.
• Illusion of Control – Believing one can control or at least influence outcomes that are actually beyond one’s control.
• Impact Bias – Overestimating the duration or intensity of the impact of an event on future feelings.
• Information Bias – Seeking information even when it does not affect action.
• Escalation of Commitment (Sunk Cost Fallacy) – Making irrational decisions based on previous rational decisions or justifying past actions, such as overbidding at auctions.
• Loss Aversion – The negative utility associated with losing an object is greater than the positive utility of acquiring it.
• Mere Exposure Effect – Expressing unreasonable preference for something simply because it is familiar.
• Moral Credential Effect – If a person is known to be unbiased, they are more likely to display bias in the future, believing their actions will be seen as blameless.
• Need for Closure – The need to reach a conclusion on an important issue, get an answer, and avoid doubt or uncertainty. Time pressure or social pressure can intensify this bias.
• Need for Contradiction – Sensational or controversial messages spread faster in the media, even if only a small percentage of scientific publications reject a consensus (e.g., climate change), but a much larger percentage of popular press articles do.
• Probability Neglect – Completely ignoring probabilistic reasoning when making decisions under uncertainty.
• Omission Bias – Judging harmful actions as worse and less moral than equally harmful inactions.
• Outcome Bias – Judging decisions based on their outcomes rather than on the quality of the decision at the time it was made (“winners are never judged”).
• Planning Fallacy – Underestimating the time required to complete tasks.
• Post-Purchase Rationalization – Convincing oneself with rational arguments that a purchase was worth the money.
• Pseudocertainty Effect – Avoiding risk when a positive outcome is expected, but taking risks to avoid a negative outcome.
• Reactance – The urge to do the opposite of what someone is trying to make you do, to protect your sense of freedom.
• Selective Perception – Expectations influence perception.
• Status Quo Bias – The desire for things to remain roughly the same.
• Unit Bias – The tendency to complete a given unit of a task, such as eating more when served larger portions.
• Von Restorff Effect (Isolation Effect) – The tendency to remember outstanding or unique items better than others.
• Zero-Risk Bias – Preferring to reduce a small risk to zero rather than significantly reducing a larger risk, even if the latter saves more lives.

Probability and Belief Biases

• Ambiguity Effect – Avoiding options where missing information makes probabilities unknown.
• Anchoring Effect – The tendency to rely too heavily on the first piece of information encountered (the “anchor”) when making decisions, such as pricing strategies in stores.
• Attentional Bias – Neglecting relevant information when judging correlations or associations.
• Availability Heuristic – Estimating the likelihood of events based on how easily examples come to mind, favoring vivid or emotionally charged memories.
• Availability Cascade – A self-reinforcing process where collective belief in something becomes more convincing through repeated public discourse (“repeat something long enough and it becomes true”).
• Clustering Illusion – Seeing patterns where none exist.
• Conjunction Fallacy – Believing that more specific conditions are more probable than general ones.
• Gambler’s Fallacy – Believing that random events are influenced by previous random events, such as expecting a coin toss to land heads after a streak of tails.
• Hawthorne Effect – People temporarily change their behavior or performance when they know they are being observed.
• Hindsight Bias – The “I knew it all along” effect; perceiving past events as having been predictable.
• Illusory Correlation – Mistaken belief in a relationship between certain actions and outcomes.
• Observer-Expectancy Effect – When a researcher’s expectations unconsciously influence the outcome of an experiment.
• Optimism Bias – Systematically overestimating the chances of success for planned actions.
• Overconfidence Effect – Overestimating one’s own abilities.
• Positive Outcome Bias – Overestimating the likelihood of positive outcomes.
• Primacy Effect – Overvaluing initial events compared to subsequent ones.
• Recency Effect – Overvaluing recent events over earlier ones.
• Regression Fallacy – Expecting extraordinary behavior to continue, rather than regress to the mean.
• Reminiscence Bump – Remembering more events from youth than from other life periods.
• Rosy Retrospection – Evaluating past events more positively than they were perceived at the time.
• Selection Bias – Bias in experimental data due to the way data was collected.
• Stereotyping – Expecting certain characteristics from a group member without knowing anything about the individual.
• Subadditivity Effect – Judging the probability of the whole as less than the probabilities of its parts.
• Subjective Validation – Perceiving something as true if one’s beliefs require it to be true, including seeing coincidences as meaningful.
• Telescoping Effect – Recent events seem more distant, and distant events seem closer in time.
• Texas Sharpshooter Fallacy – Formulating or adjusting a hypothesis after data is collected, making it impossible to test the hypothesis fairly.

Social Biases

Most of these biases are related to attribution errors.

• Actor-Observer Bias – Overemphasizing the influence of personal qualities when explaining others’ behavior, while overemphasizing situational factors for one’s own actions.
• Dunning-Kruger Effect – People with low ability at a task overestimate their ability, while highly skilled people underestimate their competence and assume others are equally skilled.
• Egocentric Bias – Believing oneself to be more responsible for the outcome of collective actions than an outside observer would judge.
• Barnum Effect (Forer Effect) – Believing that vague, general personality descriptions are highly accurate for oneself, as with horoscopes.
• False Consensus Effect – Overestimating the extent to which others agree with you.
• Fundamental Attribution Error – Overestimating the role of personal characteristics and underestimating situational influences when explaining others’ behavior.
• Halo Effect – Positive or negative traits “spill over” from one area of a person’s personality to another in the eyes of the observer.
• Herd Instinct – The tendency to adopt the opinions and follow the behavior of the majority to feel safe and avoid conflict.
• Illusion of Asymmetric Insight – Believing you know more about others than they know about you.
• Illusion of Transparency – Overestimating others’ ability to understand you, and your ability to understand others.
• Ingroup Bias – Preferring those you consider members of your own group.
• Just-World Hypothesis – Believing the world is “just” and people get what they deserve: good people are rewarded, bad people are punished.
• Lake Wobegon Effect – The tendency to believe you are above average.
• Law of Formulation Bias – The illusion that a law written as a mathematical formula is more real or valid.
• Outgroup Homogeneity Bias – Seeing members of your own group as more diverse than members of other groups.
• Projection Bias – Unconsciously assuming others share your thoughts, beliefs, values, and positions.
• Self-Serving Bias – Taking more responsibility for successes than for failures, and interpreting ambiguous information in a self-favorable way.
• Self-Fulfilling Prophecy – Engaging in behaviors that lead to outcomes that confirm your beliefs, consciously or unconsciously.
• System Justification – Defending and supporting the status quo, preferring existing social, political, and economic systems, and denying change even at the expense of individual or collective interests.
• Trait Ascription Bias – Seeing oneself as more variable in personality, behavior, and mood, while perceiving others as more predictable.
• First Impression Effect – The influence of initial opinions formed in the first moments of meeting someone on subsequent evaluations of their personality and actions.