I've been reading about the Dunning-Kruger effect (DKE) lately. For the uninitiated, this means that incompetent people not having the ability to recognize that their performance is poor (even if it's pointed out to them). This is because the skills you need to recognize poor performance are the same skills you need in order to perform well. The flip side of the DKE is that highly competent people tend to underestimate their performance relative to others (because if something is easy for them, they tend to believe it's easy for everyone). This effect has been documented many, many times.

Basic example. Many Americans say, there's two of them instead of there are two of them. They presumably believe that there's two is correct usage. Say they're given the phrase there's two of them on a grammar test. They'd mark that expression as being written correctly and would be sure they got the question right. They don't know what they don't know, and therefore are incapable of recognizing their own poor performance. Likewise, they wouldn't be able to recognize someone else's good performance. Now scale that, and you get the idea about the Dunning-Kruger effect.

I read the following information in a review article, and it applies perfectly to the debate about whether boys are inherently better at math and science:


Quote
Women, for example, tend to disproportionately leave science careers along every step of the educational and professional ladder (Seymour, 1992). We began to wonder if top-down influences on performance estimates might contribute to this pattern. Starting in adolescence, women tend to rate themselves as less scientifically talented than men rate themselves (Eccles, 1987). Because of this, women might start to think they are doing less well on specific scientific tasks than men tend to think, even when there is no gender difference in performance. Thinking they are doing less well, women might become less enthusiastic about participating in scientific activities.

We put these notions to a test by giving male and female college students a pop quiz on scientific reasoning. Before the quiz, the students were asked to rate themselves on their scientific skills, and the women rated themselves more negatively than the men did. The students’ estimates of their performance on the quiz showed the same pattern, with the women thinking that they had done less well than the men thought, even though there was no gender difference in actual performance.

In other words, males may overestimate their abilities (due to being less competent), while females underestimate their abilities (due to being more competent).

Source: Dunning D et al. (2003) Why People Fail to Recognize Their Own Incompetence Current Directions in Psychological Science 12(3): 83-87. PM me if you want a copy.