The Dunning–Kruger effect is a hypothetical cognitive bias stating that people with low ability at a task overestimate their ability.
As described by social psychologists David Dunning and Justin Kruger, the bias results from an internal illusion in people of low ability and from an external misperception in people of high ability; that is, "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". It is related to the cognitive bias of illusory superiority and comes from people's inability to recognize their lack of ability. Without the self-awareness of metacognition, people cannot objectively evaluate their level of competence.
The effect, or Dunning and Kruger's original explanation for the effect, has been challenged by mathematical analyses and comparisons across cultures.
Original study
The psychological phenomenon of illusory superiority was identified as a form of cognitive bias in Kruger and Dunning's 1999 study "Unskilled and Unaware of It: How Difficulties in Recognizing One's Own Incompetence Lead to Inflated Self-Assessments". An example derived from cognitive bias evident in the criminal case of McArthur Wheeler, who, on April 19, 1995, robbed two banks while his face was covered with lemon juice, which he believed would make him invisible to the surveillance cameras. This belief was apparently based on his misunderstanding of the chemical properties of lemon juice as an invisible ink.
Other investigations of the phenomenon, such as "Why People Fail to Recognize Their Own Incompetence", indicate that much incorrect self-assessment of competence derives from the person's ignorance of a given activity's standards of performance. Dunning and Kruger's research also indicates that training in a task, such as solving a logic puzzle, increases people's ability to accurately evaluate how good they are at it.
In Self-insight: Roadblocks and Detours on the Path to Knowing Thyself, Dunning described the Dunning–Kruger effect as "the anosognosia of everyday life", referring to a neurological condition in which a disabled person either denies or seems unaware of their disability. He stated: "If you're incompetent, you can't know you're incompetent ... The skills you need to produce a right answer are exactly the skills you need to recognize what a right answer is."
In 2011, Dunning wrote about his observations that people with substantial, measurable deficits in their knowledge or expertise lack the ability to recognize those deficits and, therefore, despite potentially making error after error, tend to think they are performing competently when they are not: "In short, those who are incompetent, for lack of a better term, should have little insight into their incompetence—an assertion that has come to be known as the Dunning–Kruger effect". In 2014, Dunning and Helzer described how the Dunning–Kruger effect "suggests that poor performers are not in a position to recognize the shortcomings in their performance".
Later studies
Dunning and Kruger tested the hypotheses of the cognitive bias of illusory superiority on undergraduate students of introductory courses in psychology by examining the students' self-assessments of their intellectual skills in inductive, deductive, and abductive logical reasoning, English grammar, and personal sense of humor. After learning their self-assessment scores, the students were asked to estimate their ranks in the psychology class. The competent students underestimated their class rank, and the incompetent students overestimated theirs, but the incompetent students did not estimate their class rank as higher than the ranks estimated by the competent group. Across four studies, the research indicated that the study participants who scored in the bottom quartile on tests of their sense of humor, knowledge of grammar, and logical reasoning, overestimated their test performance and their abilities; despite test scores that placed them in the 12th percentile, the participants estimated they ranked in the 62nd percentile.
Moreover, competent students tended to underestimate their own competence, because they erroneously presumed that tasks easy for them to perform were also easy for other people to perform. Incompetent students improved their ability to estimate their class rank correctly after receiving minimal tutoring in the skills they previously lacked, regardless of any objective improvement gained in said skills of perception. The 2004 study "Mind-Reading and Metacognition: Narcissism, not Actual Competence, Predicts Self-estimated Ability" extended the cognitive-bias premise of illusory superiority to test subjects' emotional sensitivity toward other people and their own perceptions of other people.
The 2003 study "How Chronic Self-Views Influence (and Potentially Mislead) Estimates of Performance" indicated a shift in the participants' view of themselves when influenced by external cues. The participants' knowledge of geography was tested; some tests were intended to affect the participants' self-view positively, and some were intended to affect it negatively. The participants then were asked to rate their performances; the participants given tests with a positive intent reported better performance than did the participants given tests with a negative intent.
To test Dunning and Kruger's hypotheses "that people, at all performance levels, are equally poor at estimating their relative performance", the 2006 study "Skilled or Unskilled, but Still Unaware of It: How Perceptions of Difficulty Drive Miscalibration in Relative Comparisons" investigated three studies that manipulated the "perceived difficulty of the tasks, and, hence, [the] participants' beliefs about their relative standing". The investigation indicated that when the experimental subjects were presented with moderately difficult tasks, there was little variation among the best performers and the worst performers in their ability to predict their performance accurately. With more difficult tasks, the best performers were less accurate in predicting their performance than were the worst performers. Therefore, judges at all levels of skill are subject to similar degrees of error in the performance of tasks.
In testing alternative explanations for the cognitive bias of illusory superiority, the 2008 study "Why the Unskilled are Unaware: Further Explorations of (Absent) Self-insight Among the Incompetent" reached the same conclusions as previous studies of the Dunning–Kruger effect: that, in contrast to high performers, "poor performers do not learn from feedback suggesting a need to improve".
One 2020 study suggests that individuals of relatively high social class are more overconfident than lower-class individuals.
Mathematical critique
Dunning and Kruger describe a common cognitive bias and make quantitative assertions that rest on mathematical arguments. But their findings are often misinterpreted, misrepresented, and misunderstood. According to Tal Yarkoni:
Their studies categorically didn’t show that incompetent people are more confident or arrogant than competent people. What they did show is [that] people in the top quartile for actual performance think they perform better than the people in the second quartile, who in turn think they perform better than the people in the third quartile, and so on. So the bias is definitively not that incompetent people think they’re better than competent people. Rather, it’s that incompetent people think they’re much better than they actually are. But they typically still don’t think they’re quite as good as people who, you know, actually are good. (It’s important to note that Dunning and Kruger never claimed to show that the unskilled think they’re better than the skilled; that’s just the way the finding is often interpreted by others.)
Paired measures
Mathematically, the effect relies on the quantifying of paired measures consisting of (a) the measure of the competence people can demonstrate when put to the test (actual competence) and (b) the measure of competence people believe that they have (self-assessed competence). Researchers express the measures either as percentages or as percentile scores scaled from 0 to 1 or from 0 to 100. By convention, researchers express the differences between the two measures as self-assessed competence minus actual competence. In this convention, negative numbers signify erring toward underconfidence, positive numbers signify erring toward overconfidence, and zero signifies accurate self-assessment.
A 2008 study by Joyce Ehrlinger summarized the major assertions of the effect that first appeared in the 1999 seminal article and continued to be supported by many studies after nine years of research: "People are typically overly optimistic when evaluating the quality of their performance on social and intellectual tasks. In particular, poor performers grossly overestimate their performances".
The effect asserts that most people are overconfident about their abilities, and that the least competent people are the most overconfident. Support for both assertions rests upon interpreting the patterns produced from graphing the paired measures.
The most common graphical convention is the Kruger–Dunning-type graph used in the seminal article. It depicted college students' accuracy in self-assessing their competencies in humor, logical reasoning, and grammar. Researchers adopted that convention in subsequent studies of the effect. Additional graphs used by other researchers, who argued for the legitimacy of the effect include (y–x) versus (x) cross plots and bar charts. The first two of these studies depicted college students' accuracy in self-assessing their competence in introductory chemistry, and the third depicted their accuracy in self-assessing their competence in business classes.
Some research suggests that the effect may actually be illusory, driven by ceiling/floor effects (exacerbated by measurement error) causing censoring rather than representing a true deficit in metacognition.
Cultural differences in self-perception
Studies of the Dunning–Kruger effect usually have been of North Americans, but studies of Japanese people suggest that cultural forces have a role in the occurrence of the effect. The 2001 study "Divergent Consequences of Success and Failure in Japan and North America: An Investigation of Self-improving Motivations and Malleable Selves" indicated that Japanese people tended to underestimate their abilities and to see underachievement (failure) as an opportunity to improve their abilities at a given task, thereby increasing their value to the social group.
Popular recognition
In 2000, Kruger and Dunning were awarded a satiric Ig Nobel Prize in recognition of the scientific work recorded in "their modest report". "The Dunning–Kruger Song" is part of The Incompetence Opera, a mini-opera that premiered at the Ig Nobel Prize ceremony in 2017. The mini-opera is billed as "a musical encounter with the Peter principle and the Dunning–Kruger Effect".
