Dunning–Kruger effect is a hypothetical cognitive bias stating that people with low ability at a task overestimate their own ability, and that people with high ability at a task underestimate their own 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 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.
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.
The effect, or Dunning and Kruger’s original explanation for the effect, has been challenged by mathematical analyses and comparisons across cultures.
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.