SAFEHOME.org has an article HERE
There’s a well-known phenomenon in psychology where people tend to think they are smarter than the average person. For Americans, that belief may approach certainty. A 2018 study found that 65% of Americans believe they have above-average intelligence.
In addition to about 2 in 3 Americans saying they are smarter than most other people, the study found that certainty of one’s superior intellect increased with income and education but decreased with age.
Naturally - when you weed out the smartest , the 'dumbest' also rise to the surface !
Now there are several studies available so , results may vary !