Cognitive bias
A cognitive bias is any of a wide range of observer effects identified in cognitive science and social psychology including very basic statistical, social attribution, and memory errors that are common to all human beings. Biases drastically skew the reliability of anecdotal and legal evidence.

# Overview
Bias arises from various life, loyalty and local risk and attention concerns that are difficult to separate or codify. Much of the present scientific understanding of biases stems from the work of Amos Tversky and Daniel Kahneman and their colleagues, whose experiments demonstrated distinct and replicable ways in which human judgment and decision-making differ from rational choice theory. This led to Tversky and Kahneman developing prospect theory as an alternative. Tversky and Kahneman claim that the biases they identified are at least partially the result of problem-solving using mental short-cuts or "heuristics", for instance using how readily or vividly something comes to mind as an indication of how often or how recently it was encountered (the availability heuristic). Other biases have been demonstrated in separate experiments, such as the Confirmation bias demonstrated by Peter C. Wason.
Some scientists have questioned whether all of the 'biases' are in fact errors. David Funder and Joachim Krueger have argued that some so called 'biases' may in fact be 'approximation shortcuts', which aid humans in making predictions when information is in short supply. For example, the false consensus effect may be viewed as a reasonable estimation based on a single known data point, your own opinion, instead of a false belief that other people agree with you.

# Types of cognitive biases
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 judgement of how likely something is, or of whether one thing is the cause of another. A distinctive class of biases affect memory (Schacter (1999)), 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 (Kunda (1990)), for example the desire for a positive self-image leading to Egocentric bias (Hoorens (1993)) 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 exact 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 (Hoorens (1993)) 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).
The following is a list of the more commonly studied 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.

# Practical Significance
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.
The latest advancement in decision mapping enables further empirical research on the influences of heuristics and bias on human decision making in contexts of risk and uncertainty. These techniques are presented by Facione and Facione in Thinking and Reasoning in Human Decision Making: The Method of Argument and Heuristic Analysis (The California Academic Press, 2007). This book describes the theory, technique, and application of this new analytical methodology. Among other things it shows how to construct decision maps from oral and textual expressions of individual or group decisions. A&H Method decision maps illustrate the combination of reasons-claim argument strands as well as the influences of cognitive heuristics and psychological dominance structuring which emerge from those data. Researchers can compare decision maps illustrating how many different people have made a decision about the same question (e.g. "Should I have a doctor look at this troubling breast cancer symptom I've discovered." "Why did I ignore the evidence that the project was going over budget?") and then craft potential cognitive interventions aimed at improving decision making outcomes.