(Source: Not me)

A cognitive bias is a person’s tendency to make errors in judgment based on cognitive factors, and is a phenomenon studied in cognitive science and social psychology.  Forms of cognitive bias include errors in statistical judgment, social attribution, and memory that are common to all human beings.  Such biases drastically skew the reliability of anecdotal and legal evidence.  These are thought to be based upon heuristics, or rules of thumb, which people employ out of habit or evolutionary necessity.

Biases can be distinguished on a number of dimensions.  For example, there are biases specific to groups (such as the risky shift) as well as biases at the individual level.

Some biases affect decision-making, where the desirability of options has to be considered (e.g. Sunk Cost fallacy).  Others such as Illusory correlation affect judgment of how likely something is, or of whether one thing is the cause of another.  A distinctive class of biases affect memory, such as consistency bias (remembering one’s past attitudes and behaviour as more similar to one’s present attitudes).

Some biases reflect a subject’s motivation, for example the desire for a positive self-image leading to Egocentric bias and the avoidance of unpleasant cognitive dissonance.  Other biases are due to the particular way the brain perceives, forms memories and makes judgments.  This distinction is sometimes described as “Hot cognition” versus “Cold Cognition”, as motivated cognition can involve a state of arousal.

Among the “cold” biases, some are due to ignoring relevant information (e.g. Neglect of probability), whereas some involve a decision or judgement being affected by irrelevant information (for example the Framing effect where the same problem receives different responses depending on how it is described) or giving excessive weight to an unimportant but salient feature of the problem (e.g. Anchoring).

The fact that some biases reflect motivation, and in particular the motivation to have positive attitudes to oneself accounts for the fact that many biases are self-serving or self-directed (e.g. Illusion of asymmetric insight, Self-serving bias, Projection bias).  There are also biases in how subjects evaluate in-groups or out-groups; evaluating in-groups as more diverse and “better” in many respects, even when those groups are arbitrarily-defined (Ingroup bias, Outgroup homogeneity bias).

Some cognitive biases belong to the subgroup of attentional biases which refer to the paying of increased attention to certain stimuli. It has been, for example, shown that people addicted to alcohol and other drugs pay more attention to drug-related stimuli.  Common psychological tests to measure those biases are the Stroop Task and the Dot Probe Task.

The following is a list of the more commonly studied cognitive biases.

For other noted biases, see list of cognitive biases.
  • Anchoring on a past reference.
  • Framing by using a too narrow approach and description of the situation or issue.
  • Hindsight bias, sometimes called the “I-knew-it-all-along” effect, is the inclination to see past events as being predictable.
  • Fundamental attribution error is the tendency for people to over-emphasize personality-based explanations for behaviors observed in others while under-emphasizing the role and power of situational influences on the same behavior.
  • Confirmation bias is the tendency to search for or interpret information in a way that confirms one’s preconceptions; this is related to the concept of cognitive dissonance.
  • Self-serving bias is the tendency to claim more responsibility for successes than failures. It may also manifest itself as a tendency for people to evaluate ambiguous information in a way beneficial to their interests.

Many social institutions rely on individuals to make rational judgments.  A fair jury trial, for example, requires that the jury ignore irrelevant features of the case (such as the attractiveness of the defendant), weigh the relevant features appropriately, consider different possibilities open-mindedly and resist fallacies such as appeal to emotion.  The various biases demonstrated in these psychological experiments suggest that people will fail to do all these things. However, they fail to do so in systematic, directional ways that are predictable.