A classic stereotype is that men are better at math than women, but there has been little if any solid evidence to explain this, even though women are not often found in high positions that require math. (Having worked with and been taught by female mathematicians, I know ability is not dependent on sex.) Basically the stereotype exists and the population seems to display it, but the explanation for why this could be true has not been found. One promising theory is called stereotype threat and it explains that if a woman believes the stereotype she will perform worse than what she is capable of.
Researchers at the University of Missouri-Columbia have reexamined the studies supporting stereotype threat and have found several issues with them. For example, there is a lack of male control groups and the improper application of statistical techniques in some of these studies. The researcher did what they could to correct the problems and when they did the significance of the results disappeared, showing the studies’ conclusions were wrong.
This is a major issue because of the amount of focus given to the theory. If it were to turn out stereotype threat is incorrect then school policies and funding have been wasted trying to fix a problem in the wrong place.