What is the Dunning-Kruger effect?
The Dunning-Kruger effect describes a pattern in self-assessment: people who perform poorly on a task tend to overrate their performance, and people who perform very well tend to underrate it slightly. Cornell psychologists Justin Kruger and David Dunning reported it in 1999 in a paper titled "Unskilled and Unaware of It."
Their explanation is a double burden. Someone who does not know grammar rules makes grammar mistakes and also lacks the knowledge needed to spot them. Low skill and weak metacognition come together.
- Researchers
- Justin Kruger and David Dunning, Cornell University (1999)
- Key finding
- Bottom-quartile participants placed themselves around the 62nd percentile
- Explanation
- The skills to perform well are the skills to judge performance
- Related ideas
- Metacognition, overconfidence bias, impostor phenomenon
The 1999 study
Kruger and Dunning tested Cornell undergraduates on humor, logical reasoning and English grammar, then asked them to estimate how their scores ranked against their peers.
- Participants in the bottom quartile scored around the 12th percentile on average but estimated they were around the 62nd.
- Participants in the top quartile underestimated their rank somewhat, because they assumed others found the test as easy as they did.
- When low scorers received brief training in logic, their self-assessments became more accurate. Gaining skill made their earlier mistakes visible.
The viral graph is not from the study
The well-known curve with a "Peak of Mount Stupid," "Valley of Despair" and "Slope of Enlightenment" does not appear in the original paper. The original figures are simple line charts comparing actual and perceived percentile by quartile. The popular claim that total beginners are the most confident also overstates the finding. Low performers rated themselves somewhat above average, not as experts.
The Dunning-Kruger effect is not an insult to throw at other people. The research suggests everyone is vulnerable to it in areas where they lack expertise.
Statistical criticism
- Regression and noise: researchers have shown that the "better-than-average" tendency plus random measurement error can produce a similar-looking graph (Nuhfer et al., 2016).
- Smaller than advertised: Gignac and Zajenkowski (2020) reanalyzed intelligence data and concluded that the effect is mostly a statistical artifact, with only a small genuine component.
- Dunning’s response: Dunning argues that the overestimation by low performers survives better measurement and is strongest in domains where feedback is rare.
How to calibrate your confidence
- Seek concrete feedback: grades, code reviews and edits compare your work with an outside standard.
- Explain it to someone: the point where your explanation breaks down marks the edge of your knowledge.
- Learn the standards first: knowing what experts consider "good" improves self-assessment.
- Predict, then check: write down the score you expect before a test and compare it with the result.
For another bias that distorts self-judgment, see cognitive dissonance.
Frequently asked questions
- What is the opposite of the Dunning-Kruger effect?
- Skilled people underestimating themselves. It is often linked to impostor syndrome, although the two are not the same concept.
- Is the "Mount Stupid" graph wrong?
- It is a later popular illustration, not data from the study. It can be a useful metaphor for learning, but it does not show what the research measured.
- Is the Dunning-Kruger effect real?
- Low performers overestimating themselves is a well-replicated observation, but how much of it reflects a psychological cause versus statistical artifacts is still debated.
References
- Kruger, J., & Dunning, D. (1999). Unskilled and unaware of it: How difficulties in recognizing one’s own incompetence lead to inflated self-assessments. Journal of Personality and Social Psychology, 77(6), 1121–1134.
- Dunning, D. (2011). The Dunning–Kruger effect: On being ignorant of one’s own ignorance. Advances in Experimental Social Psychology, 44, 247–296.
- Nuhfer, E., et al. (2016). Random number simulations reveal how random noise affects the measurements and graphical portrayals of self-assessed competency. Numeracy, 9(1), Article 4.
- Gignac, G. E., & Zajenkowski, M. (2020). The Dunning-Kruger effect is (mostly) a statistical artefact. Intelligence, 80, 101449.
- Ehrlinger, J., et al. (2008). Why the unskilled are unaware: Further explorations of (absent) self-insight among the incompetent. Organizational Behavior and Human Decision Processes, 105(1), 98–121.