A cognitive bias is a systematic pattern of deviation from the norm or rationality in judgment. Individuals create their own "subjective reality" from their perception of the input. An individual's construction of reality, not the objective input, may dictate their behavior in the world. Thus, cognitive biases may sometimes lead to perceptual distortion, inaccurate judgment, illogical interpretation, and irrationality.
While cognitive biases may initially appear to be negative, some are adaptive. They may lead to more effective actions in a given context.For instance: Furthermore, allowing cognitive biases enables faster decisions which can be desirable when timeliness is more valuable than accuracy, as illustrated in heuristics. Other cognitive biases are a "by-product" of human processing limitations, resulting from a lack of appropriate mental mechanisms (bounded rationality), the impact of an individual's constitution and biological state (embodied cognition), or simply from a limited capacity for information processing. Cognitive biases can make individuals more inclined to endorsing pseudoscientific beliefs by requiring less evidence for claims that confirm their preconceptions. This can potentially distort their perceptions and lead to inaccurate judgments.
A continually evolving list of cognitive biases has been identified over the last six decades of research on human judgment and decision-making in cognitive science, social psychology, and behavioral economics. The study of cognitive biases has practical implications for areas including clinical judgment, entrepreneurship, finance, and management.
Overview When making judgments under uncertainty, people rely on mental shortcuts or heuristics, which provide swift estimates about the possibility of uncertain occurrences. For example, the representativeness heuristic is defined as the tendency to judge the frequency or likelihood of an occurrence by the extent of which the event resembles the typical case. Similarly the availability heuristic is that individuals estimate the likelihood of events by how easy they are to recall, and the anchoring heuristic prefers the initial reference points that are recalled. While these heuristics are efficient and simple for the brain to compute, they sometimes introduce predictable and systematic cognitive errors, or biases.
The "Linda Problem" illustrates the representativeness heuristic and corresponding bias. Participants were given a description of "Linda" that suggests Linda might well be a feminist (e.g., she is said to be concerned about discrimination and social justice issues). They were then asked whether they thought Linda was more likely to be (a) a "bank teller" or (b) a "bank teller and active in the feminist movement". A majority chose answer (b). Independent of the information given about Linda, though, the more restrictive answer (b) is under any circumstance statistically less likely than answer (a). This is an example of the conjunction fallacy: respondents chose (b) because it seemed more "representative" or typical of persons who might fit the description of Linda. If they assumed that choosing (a) would entail Linda not being active in the feminist movement, that would be a pragmatic implicature. The representativeness heuristic may lead to errors such as activating stereotypes and inaccurate judgments of others.
Gerd Gigerenzer argues that heuristics should not lead us to conceive of human thinking as riddled with irrational cognitive biases. They should rather conceive rationality as an adaptive tool, not identical to the rules of formal logic or the probability calculus. Gigerenzer believes that cognitive biases are not biases, but rules of thumb, or as he would put it "gut feelings" that can actually help us make accurate decisions in our lives. There is not clear evidence that these behaviors are genuinely, severely biased once the actual problems people face are understood. Advances in economics and cognitive neuroscience now suggest that many behaviors previously labeled as biases might instead represent optimal decision-making strategies.
Definitions Definition Source "bias ... that occurs when humans are processing and interpreting information" ISO/IEC TR 24027:2021(en), 3.2.4, ISO/IEC TR 24368:2022(en), 3.8"...we can define cognitive biases as systematic errors in cognition that occur when, having an epistemic goal, we non-consciously deviate from it by relying on irrelevant or partially relevant information and ignoring that which is relevant."Nadurak V. (2025). Heuristics and cognitive biases: A conceptual analysis. Memory & cognition, 10.3758/s13421-025-01814-w. Advance online publication. https://doi.org/10.3758/s13421-025-01814-w
History The notion of cognitive biases was introduced by Amos Tversky and Daniel Kahneman in 1972 and grew out of their experience of people's innumeracy, or inability to reason intuitively with the greater orders of magnitude. Tversky, Kahneman, and colleagues demonstrated several replicable ways in which human judgments and decisions differ from rational choice theory. Their 1974 paper, Judgment under Uncertainty: Heuristics and Biases, outlined how people rely on mental shortcuts when making judgments under uncertainty. Experiments such as the "Linda problem" grew into heuristics and biases research programs, which spread beyond academic psychology into other disciplines including medicine and political science.
The list of cognitive biases has long been a topic of critique. In psychology a "rationality war" unfolded between Gerd Gigerenzer and the Kahneman and Tversky school, which pivoted on whether biases are primarily defects of human cognition or the result of behavioural patterns that are actually adaptive or "ecologically rational". Gerd Gigerenzer has historically been one of the main opponents to cognitive biases and heuristics. This debate has recently reignited, with critiques arguing there has been an overemphasis on biases in human cognition.
A kind of middle ground was put forward by Martie Haselton and David Buss, which acknowledges both the defect and adaptivity of cognitive biases. In this model, evolution favors a bias toward the least costly error. introduced the concept of cognitive bias modification, which focuses on reducing maladaptive cognitive patterns through computer-based attention training and behavioral tasks.
Types Biases can be distinguished on a number of dimensions. Examples of cognitive biases include - Biases specific to groups (such as the risky shift) versus biases at the individual level. Biases that affect decision-making, where the desirability of options has to be considered (e.g., sunk costs fallacy). Biases, such as illusory correlation, that affect judgment of how likely something is or whether one thing is the cause of another. Biases that affect memory, such as consistency bias (remembering one's past attitudes and behavior as more similar to one's present attitudes). Biases that 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 reasoning can involve a state of arousal. Among the "cold" biases,
some are due to ignoring relevant information (e.g., neglect of probability), some involve a decision or judgment being affected by irrelevant information (for example the framing effect where the same problem receives different responses depending on how it is described; or the distinction bias where choices presented together have different outcomes than those presented separately), and others give excessive weight to an unimportant but salient feature of the problem (e.g., anchoring).
As some biases reflect motivation specifically the motivation to have positive attitudes to oneself. It accounts for the fact that many biases are self-motivated or self-directed (e.g., illusion of asymmetric insight, self-serving 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 refers to paying increased attention to certain stimuli. It has been shown, for example, 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. Individuals' susceptibility to some types of cognitive biases can be measured by the Cognitive Reflection Test (CRT) developed by Shane Frederick (2005).
List of biases
The following is a list of the more commonly studied cognitive biases: