Psychology › Thinking, memory & biases › Overconfidence
Dunning–Kruger effect
1999· Finding or experiment
Mixed evidenceSome support; effects smaller or less consistent than once thought.
The finding that people with the least skill in an area tend to overestimate their ability the most.
See it on the Psychology map →What it says
In 1999 Justin Kruger and David Dunning at Cornell tested students on logic, grammar and humor, then asked how they had done. Those scoring around the 12th percentile placed themselves near the 62nd; top scorers slightly underrated themselves. Their explanation: the skills needed to do something well are the same skills needed to judge it, so the unskilled cannot see their mistakes. The popular 'Mount Stupid' curve, where beginners feel most confident, is not in their data.
Why it matters
It warns that confidence is a poor guide to competence, especially for novices. For a new investor, an outside track record and honest feedback beat one's own sense of skill.
The evidence
Status: mixed evidence. That low performers overestimate more replicates widely, but critics show regression to the mean and a general better-than-average bias can create much of the classic chart, even from random numbers.
Open questions
How much is genuine lack of insight versus statistical artifact; estimates of the true effect, once the statistics are handled carefully, range from substantial to small.
Connections (2)
▸Dunning–Kruger effect was statistically re-examined during The replication crisisMixed evidence
The connection
During psychology's replication audit, critics re-examined the Dunning–Kruger chart. Statisticians showed that regression to the mean plus the general tendency to rate oneself above average can produce much the same picture, even from random numbers. The effect did not simply fail to replicate; the dispute is over how much of it is real psychology rather than measurement.
Who showed it and when
Critiques began with Joachim Krueger and Ross Mueller in 2002 and revived after 2016, notably in Gilles Gignac and Marcin Zajenkowski's 2020 study of about 930 people.
How solid is it?
Simulations reproduce the classic chart from random data; defenders, such as Joyce Ehrlinger and colleagues (2008), found the gap survived corrections for measurement error.
Open questions
Whether low performers truly lack insight or simply guess near average, and how large the effect is once the statistics are handled properly.
▸Dunning–Kruger effect is a claimed special case of OverconfidenceMixed evidence
The connection
Overconfidence is the broad tendency to overrate our knowledge, skill and precision. Dunning and Kruger argued for a specific version: the least skilled overrate themselves most, because the skill needed to perform is the same skill needed to judge performance. In their tests, low scorers near the 12th percentile placed themselves around the 62nd.
Who showed it and when
Justin Kruger and David Dunning, Cornell University, 1999, testing undergraduates on logic, grammar and humor.
How solid is it?
The original four studies and many repeats show low performers overestimate most; but statistics alone, through regression to the mean, explain part of the pattern.
Open questions
Whether novices' large overestimates and experts' slight underestimates reflect different kinds of thinking, or the same general bias plus measurement noise.