From yee Wiki:
The Dunning–Kruger effect is a cognitive bias in which unskilled individuals suffer from illusory superiority, mistakenly rating their ability much higher than is accurate. This bias is attributed to a metacognitive inability of the unskilled to recognize their ineptitude. 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."
The phenomenon was first tested in a series of experiments published in 1999 by David Dunning and Justin Kruger of the Department of Psychology, Cornell University. They 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:
1.tend to overestimate their own level of skill;
2.fail to recognize genuine skill in others;
3.fail to recognize the extremity of their inadequacy;
4.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.
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.
Research conducted by Burson et al (2006) set out to test one of the core hypotheses put forth by Kruger and Muller in their paper "Unskilled, unaware, or both? The better-than-average heuristic and statistical regression predict errors in estimates of own performance," "that people at all performance levels are equally poor at estimating their relative performance."
In order to test this hypothesis, the authors investigate three different studies, which all manipulated the "perceived difficulty of the tasks and hence participants’ beliefs about their relative standing."
The authors found that when researchers presented subjects with moderately difficult tasks that the best and the worst performers actually varied little in their ability to accurately predict their performance. Additionally, they found that with more difficult tasks, the best performers are less accurate in predicting their performance than the worst performers. The authors conclude that these findings suggest 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. East Asians tend to underestimate their abilities, and see underachievement as a chance to improve themselves and get along with others.
Although the Dunning–Kruger effect was put forward in 1999, Dunning and Kruger have noted similar historical observations from philosophers and scientists, including Confucius ("Real knowledge is to know the extent of one's ignorance."), 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", though this is actually a misquote, see Wikiquote), and Charles Darwin, whom they quoted in their original paper ("ignorance more frequently begets confidence than does knowledge").
Geraint Fuller, commenting on the paper, noted that Shakespeare expressed similar sentiment in As You Like It ("The Foole doth thinke he is wise, but the wiseman knowes himselfe to be a Foole." (V.i)).