It would be impossible for the proportions of intelligent and unintelligent people to be unequal, because IQ scores are normed so that half the people are above average intelligence and half are below. (For the same reason, the number of short people is the same as the number of tall people, provided height is normally distributed.)
However, most people believe they are more intelligent than they are. This overconfidence was captured in a famous study by Justin Kruger and David Dunning at Cornell University. The researchers administered a 20-item test on logical reasoning skills to 45 undergraduates. After the test, the students were asked to estimate:
• their percentile rank in logical thinking relative to all their classmates
• their score on the test (as a percentile) relative to all their classmates
• how many questions out of the 20 that they answered correctly.
On comparing the actual test score of each student with his or her perceived logical ability relative to others, the researchers reported:
Participants in general overestimated their logical reasoning ability, and it was those in the bottom quartile who showed the greatest miscalibration.
The data showed that those with the lowest level of competence in logical reasoning were the most overconfident in their abilities. This result, now known as the Dunning–Kruger effect is displayed in the figure below, where the graph takes a downward dip as competence increases. The upward swing in the curve shows that overconfidence was less pronounced among those of higher logical ability.
Although individuals with the greatest logical reasoning ability had more confidence than average, they overestimated the abilities of others, and therefore underestimated their own ability relative to others. In a 2004 study that was expanded to include a broad variety of intellectual and physical skills, Dunning et al. found:
The correlation between self-ratings of skill and actual performance in many domains is moderate to meager…People overrate themselves. On average, people say that they are “above average” in skill (a conclusion that defies statistical possibility), overestimate the likelihood that they will engage in desirable behaviors and achieve favorable outcomes, furnish overly optimistic estimates of when they will complete future projects, and reach judgments with too much confidence.
The researchers explained that a certain amount of expertise in a field or skill is required to recognize your deficiencies. This principle was recognized by Alexander Pope in 1711, in his famous An Essay on Criticism:
A little learning is a dangerous thing
Drink deep, or taste not the Pierian spring
There shallow draughts intoxicate the brain,
And drinking largely sobers us again.
In essence, the reason that most people overestimate their intelligence relative to others is that they are unaware of the information that they are missing. The highly intelligent, on the other hand, usually recognize the vastness of what is unknown to them and acquire a humility about the knowledge and acuity they possess. Sir Isaac Newton, having laid the foundations for modern science and received all the honors that a scholar could wish for, asserted:
I do not know what I may appear to the world; but to myself I seem to have been only like a boy playing on the seashore, and diverting myself in now and then finding a smother pebble or prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me.
