A study that proves what we've suspected all along...

"Not only do the incompetent reach erroneous conclusions and make unfortunate choices, but their incompetence robs them of the ability to realize it."

--Justin Kruger, assistant professor of psychology at the University of Illinois, and David Dunning, professor of psychology at Cornell University, on people who do things badly but think they do them well, New York Times, Jan. 18.

The Hypothesis:

incompetent individuals tend to overestimate their own level of skill.

incompetent individuals fail to recognize genuine skill in others.

incompetent individuals fail to recognize the extremity of their inadequacy.

if they can be trained to substantially improve their own skill level, these individuals can recognize and acknowledge their own previous lack of skill.

The results:
Across 4 studies, the authors found that participants scoring in the bottom quartile on tests of humor, grammar, and logic grossly overestimated their test performance and ability. Meanwhile, people with true knowledge tended to underestimate their competence.

APA Journal Well worth the read.

Or, you can take a look at the WIKIPEDIA article.