Cognitive Biases List

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The following is a listing of the more common Cognitive Biases.


Actor-Observer Bias: when it comes to explaining other people’s behavior, people overemphasize the influence of personality and underemphasize the influence of circumstances, but do the opposite when it comes to explaining their own behavior. People thus see themselves as flexible and responsive to circumstances but see others as fixed in their ways. This is also sometimes referred to as a Trait Ascription Bias.

Ambiguity Bias: people tend to select options for which they can estimate the probability of the outcome over those for which they are unable to make any such estimate. People tend to avoid options for which they don’t have adequate information.

Anchoring or Focusing Bias: people tend to rely heavily on one particular piece of information when making decisions, often a piece of information they obtained early on. For example people often make big purchase decisions, such as for a house or car, on some relatively minor feature. This is often deliberately used by those who wish to manipulate us as they seek to plant some particular idea in our head that favors their position.

The anchoring and adjustment process is where we begin by anchoring on the most easily retrievable relevant number and then adjust up and down based on information available. However our adjustments tend to be ‘sticky’ and stay relatively close to our anchor, thus if the initial anchoring number is not appropriate then we will not get to a reasonable outcome. This is often exploited by salesmen. Where a negotiation starts can well be the primary influence on where it ends up.

Attention Bias: we notice far less of what is going on around us than we realize, and we tend to only really notice that which we are explicitly paying attention to. For much of the rest of what we believe we are seeing, the background, our brains is often filling out the detail based on past experiences rather than based on what is really there. The more you are paying attention to something in particular the less likely you are to notice something unusual in the background.

The Attribution Bias: if I make a mistake or do something wrong there is a good reason, and I am innocent; if others make the same mistake or do wrong they are guilty and should accept the consequences.

Availability Bias: people overestimate probabilities based on the fact that they can bring particular examples to mind, and tend to be much more influenced by information that is readily to hand. This includes a tendency to be more persuaded by information presented in a visual form rather than that provided as a relatively long piece of text, and also to be more influenced by information that produces strong emotions or is otherwise dramatic.

Bandwagon Effect Bias: as more people come to believe in something, others jump on the bandwagon without thinking too much about it, either because they want to conform, or because they are lazy in their thinking and take the view that something popular must be right, particularly if it is advantageous to themselves in some way.

The Barnum Effect Bias: individuals will readily accept as highly accurate, descriptions of their personality that are supposedly tailored specifically for them, even though the descriptions are in fact vague and general enough to apply to a wide range of people.

Belief Bias: people’s evaluation of the strength of an argument is strongly influenced by whether they are already prejudiced towards or against the conclusion. If they don’t agree with the conclusion they are more likely to reject what is actually a good argument, and similarly accept poor arguments if they agree with the conclusion.

Benefit Bias: people generally view something that would be of benefit to them as less risky than they would do if it had been neutral or disadvantageous to them.

Blind Spot Bias: people see themselves as generally ‘better than average’ when it comes to having positive traits and ‘less than average’ for negative traits. This includes believing themselves to be less prone to biases than most other people.

Even-Chance Bias: many people believe that chance events even themselves out such that if, for example, a sequence of 13 heads occurred on a coin toss, they will believe that for a while afterwards it is more likely that tails will occur, so as to even out the run of heads. This is not the case.

Choice Supportive Bias: our memories are not absolutely true and become distorted. The distortion is strongly biased towards seeing ourselves in a positive ego enhancing light, and we often believe that we were right in our past beliefs and decisions. For example we believe we knew things would turn out the way they did before they did. In reality we didn’t have any more idea than anyone else, but once things have happened we remember any thought we might have had towards the way things turned out and forget the thoughts we had about alternatives. It is not particularly unusual to have completely false memories, or to remember as our own beliefs things we might have read or been told by others.

Clustering Bias: people underestimate the likelihood of patterns in random events and see them as having significance. It’s because they underestimate how many different patterns there can be.

Conservativism Bias: people tend to cling to their existing views at the expense of acknowledging new information. This is also where people tend to underestimate high values and high probabilities and overestimate low ones.

Confirmation or Preconception Bias: people give greater weight to information that confirms their beliefs or is otherwise advantageous to them. They tend to interpret ambiguous evidence, and evidence on its own is often ambiguous, in their own favor, and ignore or undervalue evidence that goes against their beliefs. In a particularly suspicious atmosphere, confirmation bias can even lead to the absence of information being seen as a confirmation.

Congruence Bias: people place greater reliance on direct testing of a hypothesis than on indirect testing (ie. a test which eliminates alternatives leaving only the one hypothesis remaining). This can lead to bias when there are a number of hypothesis some of which can be directly tested whilst other cannot. Better to focus on tests that would differentiate between the hypotheses. Note that Sherlock Holmes clearly did not suffer from this bias with the famous quote: “when you have eliminated the impossible, whatever remains, however improbable, must be the truth”.

Consistency Bias is the tendency to believe we were always the way we are now. When our attitudes or beliefs change we tend to alter our memories to be consistent with our changed attitudes or beliefs.

Contrast Bias is when we perceive something as more extreme than it is as a result of having just been exposed to something else with the same characteristic but a different value. Thus the same water may seem to us hot or cold depending on whether we had just been exposed to more extreme cold or more extreme hot water. Or if we are interviewing candidates and we interview a particularly good (or bad) candidate, the next candidate is likely to be perceived as worse (or better) than they really are. Contrast Bias can be a particular issue with regards decision-making because the idea or option that arrives right after a bad idea or option will tend to be rated much better than it would have been rated if presented at a different time.

Control Bias is where people underestimate risks if they believe they can control them.

Distinction Bias is the tendency to see two items as more dissimilar when evaluating them together than when evaluating them separately. Our mind exaggerates the differences as a means of distinguishing the items. Thus if viewing the quality of two TV screens next to each other one may appear significantly worse, whilst if we’d seen them at separate times we might not have noticed the difference. Or if we get a good suggestion for a solution after a bad suggestion, we tend to rate the good solution as much better than it might actually be. This is used as an influencing technique when we are pushed towards one option in particular because of the way it is presented together or alongside other options.

Early Evidence Bias: information that appears earlier is weighted more strongly than information that appears later. Note however there is also the Recency bias where recent information is also more heavily weighted. Between them the Early Evidence bias, sometimes referred to as the Primacy bias, and the Recency bias, lead to bias against information in the middle.

Early Reward Bias is when given two similar rewards, people show a preference for the one expected to arrive sooner rather than the one expected to arrive later. We are said to ‘discount’ the value of the later reward; the more so the longer the delay.

Egocentric Bias is when people see their role in things as more prominent than they actually were. For example claiming a greater role for themselves in joint action or in meetings, or remembering past events in a far more favorable light with regards themselves than was actually the case.

Endowment Bias is our tendency to place more value on something we own than on something we don’t own. As a result people will demand more to give up something they own than they would be willing to pay to acquire it.

Extreme Aversion Bias is the tendency to avoid extremes and to choose something in between.

Observer Expectancy Bias occurs when someone subtly and unintentionally communicates their expectations of an outcome, which then causes biased behavior in another person. The wording of a question for example can subtly suggest an expected or preferred response. With regards undertaking experiments or tests involving people, this unconscious influencing of participants by the experimenter is termed The Experimenter Expectancy Bias.

Expectation Bias is where we see what we expect to see even when it is not there.

False consensus Bias is the tendency of a person to overestimate how much other people agree with them.

Familiarity Bias is where we notice and are more positively disposed to things we recognize or are familiar with. We give more weight to the correctness of something we are familiar with, and tend to reject or disbelieve things we are unfamiliar with.

The Framing Bias is when we look at a situation from a particular viewpoint and fail to recognize there are other viewpoints which might enable us to think differently about it.

The Frequency illusion is where something that has recently come to our attention then appears to be everywhere, with far greater apparent frequently than previously.

The Halo Effect Bias is a tendency to view a person or thing favorably, or unfavorably, based on a single incident or trait.

Hindsight Bias is the tendency for people to believe they knew it all along after a given event has occurred. This can even lead to memory distortions as people often fool themselves about what they really believed at the time before the outcome became what it became. Given any event, after it has occurred most people seemed to have ‘known it all along,’ even though few of them seem to have been so definitive prior to the event occurring.

An Illusion of Control Bias is the tendency for people to overestimate their ability to control events which are in fact largely determined by chance. They thus praise or criticize themselves for outcomes over which in reality they had little or no say. Many gamblers suffer badly from this bias.

Implicit Assumption Bias is where an opinion is implicitly taken as though it were fact. This is often expressed through use of certain adjectives such as ‘he justifiably …’, or ‘it is obviously the case that …’.

Information Bias is the belief that the more information that can be acquired in support of making a decision the better, even though often the more information is irrelevant to the decision.

Ingroup Bias is the tendency for people to give greater weight or preference to those who are members of groups of which they are themselves members.

A Just World Bias is where people believe that the world is essentially fair, and as a result those who are poor or are suffering or are victims, have, in some way, only themselves to blame. This can readily lead to prejudices and discrimination.

A Negativity Bias is the tendency for people to pay more attention or give more weight to negative information or experiences than to positive. Thus a piece of negative information about someone or something will outweigh an equivalent piece of positive information. A good and a bad experience of similar weight occurring together will leave one feeling down rather than up or neutral. People tend to notice risks or threats more readily than they notice opportunities.

The Normalcy Bias is where people who are experiencing extreme circumstances significantly underplay the seriousness of the situation, seizing on any ambiguities as signs that things aren’t as serious as they in fact are.

Omission Bias is our tendency to see harmful actions as being worse than equally harmful inactions.

Optimism Bias is the tendency for some people to overestimate the likelihood of positive events and underestimating the likelihood of negative events. It is, for example, a continual problem when planning projects based on subjective estimates of how long things take.

Outcome Bias, strongly linked to hindsight bias, is when a decision is judged based upon how it turned out rather than what could reasonably have been known at the time the decision was made.

The Overconfidence Bias is our tendency to be overconfident in our judgments. We all suffer from it to some extent, some more so than others. For example over 90% of drivers rate themselves as better than average. People who were 100% confident in their spelling of certain words were in fact only right 80% of the time. Most people are overconfident in their ability to accurately assess risks.

Partsum Bias is the tendency to estimate the probabilities of parts of a whole as summing up to more than estimates of the probability of the whole itself.

Pattern Bias is our tendency to see patterns even where they don’t exist. Thus we readily see images of faces or animals in clouds. Or we interpret vague statements such as given in astrological predications as specific to us because we focus on aspects that match and ignore those that don’t or fail to realize that statements are so general anyone could find a match.

Personal Validation Bias is where a person is more likely to consider information to be correct if it has some personal meaning or significance to them. People will often give far more weight to personal experiences and anecdotes than they will to objectively measured probabilities.

Pessimism Bias is the tendency of some people to overestimate the likelihood of negative things happening.

Recall Bias is where we estimate as more probable things we find interesting or memorable. When we can recall specific examples of an event, we generally believe it is more common than it really is. Similarly if we cannot think of examples of an event we judge its probability to be lower than it really is. Thus chance or coincidental events that are memorable are often judged to be far more common than they really are.

Recency Bias is where more recent information will tend to push out older information, and thus we are more likely to be influenced by it. Albeit noting the Early Evidence bias where early information is also more readily remembered. To keep an appropriate balance we need to ensure we keep good notes and review them regularly, so that newer or more readily remembered information doesn’t inappropriately bias our decisions.

Restraint Bias is the tendency for people to overestimate their self-control, and thus they are more likely to put themselves in the way of temptation.

Risk Framing Bias is the fact that people tend to be more risk adverse when faced with positive options, but more likely to take risks when faced with negative options. Thus people are less likely to take chances when looking to gain something than when faced with losing something.

Secrecy Bias is when people give greater weighting to information that they believe is restricted and not openly available in some way.

Selective Outcome Bias occurs when we only use the results that favor our viewpoint and suppress those that don’t. If you run 10 sampling tests then you will get a spread of results. If you then only present the results from one test at the extreme you will get a biased viewpoint.

Social Comparison Bias is claiming an argument on the basis of some social comparison, such as a parent claiming they are right because they are the parent and the other the child.

Unconscious Bias is the tendency to make unconscious assumptions about another person based upon a single characteristic, such as their sex, gender, place of origin, etc. It is a natural process and the fact that we are subject to it does not make us prejudiced, because we are all subject to it to a greater or lesser degree. However we should be aware of it, and actively seek to compensate for it, and when we don’t then we are being prejudiced. Thus whenever we find ourselves having reservations about someone that we don’t have personal experiences of interacting with, then there is likely to be unconscious bias at work.

The Zeigarnik Effect is a bias towards wanting to complete unfinished tasks, and the fact that we haven’t can keep intruding on our consciousness when trying to do other things. It can be more extreme in some people and lead to them going out of their way to get something finished even when there are more important things to be done.