The Dunning–Kruger effect is a cognitive bias in which unskilled individuals suffer from illusory superiority, mistakenly rating their ability much higher than average. This bias is attributed to a metacognitive inability of the unskilled to recognize their mistakes.
Actual competence may weaken self-confidence, as competent individuals may falsely assume that others have an equivalent understanding. David Dunning and Justin Kruger of Cornell University conclude, "the miscalibration of the incompetent stems from an error about the self, whereas the miscalibration of the highly competent stems from an error about others".
Historical references 
Although the Dunning–Kruger effect was put forward in 1999, Dunning and Kruger quoted Charles Darwin ("Ignorance more frequently begets confidence than does knowledge") and Bertrand Russell ("One of the painful things about our time is that those who feel certainty are stupid, and those with any imagination and understanding are filled with doubt and indecision") as authors who have recognised the phenomenon. Geraint Fuller, commenting on the paper, notes that Shakespeare expresses similar sentiment in As You Like It ("The fool doth think he is wise, but the wise man knows himself to be a fool." (V.i)).
The hypothesized phenomenon was tested in a series of experiments performed by Dunning and Kruger. Dunning and Kruger noted earlier studies suggesting that ignorance of standards of performance is behind a great deal of incompetence. This pattern was seen in studies of skills as diverse as reading comprehension, operating a motor vehicle, and playing chess or tennis.
Dunning and Kruger proposed that, for a given skill, incompetent people will:
- tend to overestimate their own level of skill;
- fail to recognize genuine skill in others;
- fail to recognize the extremity of their inadequacy;
- recognize and acknowledge their own previous lack of skill, if they are exposed to training for that skill.
Dunning has since drawn an analogy ("the anosognosia of everyday life") with a condition in which a person who suffers a physical disability because of brain injury seems unaware of or denies the existence of the disability, even for dramatic impairments such as blindness or paralysis.
Supporting studies 
Dunning and Kruger set out to test these hypotheses on Cornell undergraduates in psychology courses. In a series of studies, they examined the subjects' self-assessment of logical reasoning skills, grammatical skills, and humor. After being shown their test scores, the subjects were again asked to estimate their own rank: the competent group accurately estimated their rank, while the incompetent group still overestimated theirs. As Dunning and Kruger noted,
- Across four studies, the authors found that participants scoring in the bottom quartile on tests of humor, grammar, and logic grossly overestimated their test performance and ability. Although test scores put them in the 12th percentile, they estimated themselves to be in the 62nd.
Meanwhile, people with true ability tended to underestimate their relative competence. Roughly, participants who found tasks to be relatively easy erroneously assumed, to some extent, that the tasks must also be easy for others.
A follow-up study, reported in the same paper, suggests that grossly incompetent students improved their ability to estimate their rank after minimal tutoring in the skills they had previously lacked, regardless of the negligible improvement in actual skills.
In 2003, Dunning and Joyce Ehrlinger, also of Cornell University, published a study that detailed a shift in people's views of themselves when influenced by external cues. Participants in the study, Cornell University undergraduates, were given tests of their knowledge of geography, some intended to affect their self-views positively, some negatively. They were then asked to rate their performance, and those given the positive tests reported significantly better performance than those given the negative.
Daniel Ames and Lara Kammrath extended this work to sensitivity to others, and the subjects' perception of how sensitive they were. Other research has suggested that the effect is not so obvious and may be due to noise and bias levels. In a series of 12 tasks across three studies, researchers found that on moderately difficult tasks, the best and worst performers differ very little in accuracy, and on more difficult tasks, the best performers are less accurate than the worst performers in their judgments. This pattern suggests that judges at all skill levels are subject to similar degrees of error.
Ehrlinger et al. (2008) made an attempt to test alternative explanations, but came to qualitatively similar conclusions to the original work. The paper concludes that the root cause is that, in contrast to high performers, "poor performers do not learn from feedback suggesting a need to improve."
Studies on the Dunning–Kruger effect tend to focus on American test subjects. A study on some East Asian subjects suggested that something like the opposite of the Dunning–Kruger effect may operate on self-assessment and motivation to improve.
Dunning and Kruger were awarded the 2000 satirical Ig Nobel Prize in Psychology for their paper, "Unskilled and Unaware of It: How Difficulties in Recognizing One's Own Incompetence Lead to Inflated Self-Assessments".
See also 
- Anton–Babinski syndrome
- Curse of knowledge
- Crank (person)
- Depressive realism
- Downing effect
- Four stages of competence
- Hanlon's razor
- I know that I know nothing
- Illusory superiority
- Impostor syndrome
- Overconfidence effect
- Peter Principle
- Self-serving bias
- Superiority complex
- Morris, Errol (20 June 2010). "The Anosognosic's Dilemma: Something's Wrong but You'll Never Know What It Is (Part 1)". New York Times. Retrieved 7 March 2011.
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- Charles Darwin (1871). "The Descent of Man" (w). pp. Introduction, page 4. Retrieved 18 July 2008.
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- Dunning, David, “Self-Insight: Roadblocks and Detours on the Path to Knowing Thyself (Essays in Social Psychology),” Psychology Press: 2005, pp. 14–15. ISBN 1-84169-074-0
- Joyce Ehrlinger; David Dunning (January 2003). "How Chronic Self-Views Influence (and Potentially Mislead) Estimates of Performance". Journal of Personality and Social Psychology (American Psychological Association) 84 (1): 5–17. doi:10.1037/0022-35188.8.131.52. PMID 12518967.
- Daniel R. Ames; Lara K. Kammrath (September 2004). "Mind-Reading and Metacognition: Narcissism, not Actual Competence, Predicts Self-Estimated Ability" (PDF). Journal of Nonverbal Behavior 28 (3): 187–209. doi:10.1023/B:JONB.0000039649.20015.0e. Retrieved 29 December 2012.
- Burson, K.; Larrick, R.; Klayman, J. (2006). "Skilled or unskilled, but still unaware of it: how perceptions of difficulty drive miscalibration in relative comparisons". Journal of Personality and Social Psychology 90 (1): 60–77. doi:10.1037/0022-35184.108.40.206. PMID 16448310. hdl:2027.42/39168.
- DeAngelis, Tori (feb 2003). "Why we overestimate our competence". Monitor on Psychology (American Psychological Association) 34 (2): 60. Retrieved 7 March 2011.
- "Ig Nobel Past Winners". Retrieved 7 March 2011.