The Dunning-Kruger effect occurs when incompetent people not only fail to realise their incompetence, but consider themselves much more competent than everyone else. Basically – they’re too stupid to know that they’re stupid.
The Dunning-Kruger effect is a slightly more specific case of the bias known as illusory superiority, where people tend to overestimate their good points compared to others. The effect has been shown by experiment in several ways. Dunning and Kruger tested students on a series of criteria such as humour, grammar and logic and compared the actual test results with each student’s estimations of their performance. Those who scored lowest on the test, in the bottom quartile, were found to have “grossly overestimated” their scores. Conversely, those with the highest scores underestimated their performance in comparison to others.
The Dunning–Kruger effect is a cognitive bias in which unskilled people make poor decisions and reach erroneous conclusions, but their incompetence denies them the metacognitive ability to recognize their mistakes. The unskilled therefore suffer from illusory superiority, rating their ability as above average, much higher than it actually is, while the highly skilled underrate their own abilities, suffering from illusory inferiority. Actual competence may weaken self-confidence, as competent individuals may falsely assume that others have an equivalent understanding. As Kruger and Dunning 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 effect is about paradoxical defects in cognitive ability, in oneself and others. [wikipedia]
The tendency for those who scored well to underestimate their performance was explained as a form of psychological projection: those who found the tasks easy (and thus scored highly) mistakenly thought that they would also be easy for others. This is similar to “impostor syndrome” — found notably in graduate students and high achieving women — whereby high achievers fail to recognise their talents as they think that others must be equally good.
And what about the underachievers who overestimated their performance? In the words of Dunning and Kruger, “this overestimation occurs, in part, because people who are unskilled in these domains suffer a dual burden: Not only do these people reach erroneous conclusions and make unfortunate choices, but their incompetence robs them of the metacognitive ability to realize it.”
The effect can also be summarised by the phrase “a little knowledge is a dangerous thing”. A small amount of knowledge can mislead a person into thinking that they’re an expert because this small amount of knowledge isn’t a well known fact. For a potent example, consider former children’s TV presenter and science advocate Johnny Ball, who in 2009 stunned audiences by denying the existence of climate change. His reasoning was based on the fact that water vapour is a more powerful greenhouse gas than carbon dioxide — and because combustion reactions also produce water, it should be water we’re worried about, not carbon dioxide. Sound reasoning to an amateur, but anyone minimally qualified in atmospheric chemistry would tell you that the water isn’t a problem because the atmosphere has a way of getting rid of excess water — it’s called “rain”. Thus its concentration (for given temperatures and pressures) remains more or less constant globally