The Dunning–Kruger effect doesn't say what most people think it says.
It's usually quoted as 'stupid people are too stupid to know it'. The 1999 study said something narrower: people who do badly at a specific task tend to overrate how well they did. They still feel less confident than experts. And some researchers think much of the effect is a statistical mirage.
David Dunning and Justin Kruger, psychologists at Cornell, published their study in 1999. They tested undergraduates on logical reasoning, English grammar and judging what is funny, then asked the students to rate their own performance. Those in the bottom quarter had scores around the 12th percentile but, on average, placed themselves around the 62nd.
The popular version stretches this a long way. The effect concerns skill at particular tasks, not general intelligence, and it does not claim that poor performers feel as confident as strong ones. Their self-ratings are inflated, but still lower than those of top performers. Some researchers also describe a mirror effect: highly skilled people tend to slightly underrate themselves relative to others, perhaps because they assume others find the task as easy as they do.
Why it happens is disputed. The original explanation is metacognitive: the skills you need to do something well are often the same skills you need to notice you are doing it badly, a 'dual burden'. A rival account says the pattern is largely statistical. When self-estimates and real scores are imperfectly correlated, the lowest scorers will almost automatically look overconfident, a case of regression toward the mean. Add the general tendency to think we are better than average and simulated data can reproduce much of the classic chart. Dunning has defended the work, arguing that people's misjudgements are real whatever their cause.
The irony was not lost on anyone. In 2000 the pair received a satirical Ig Nobel Prize for their 'modest report'. The idea has older roots too: Darwin observed that ignorance more often breeds confidence than knowledge does. The more useful lesson may be humbler than the meme: everyone is a beginner at something, and feedback beats self-assessment.
Source: Wikipedia — Dunning–Kruger effect · Text summarised from Wikipedia (CC BY-SA 4.0)
