There's a big gap between opportunities in STEM (science, technology, engineering, and math) fields for men and women, and a new study sheds light on one possible reason: Male students constantly underestimate their female peers.

University of Washington researchers surveyed 1,700 undergraduate biology students about their peers' performance. While women's ratings of both men and women matched their peers' grades, men consistently ranked their male peers above their female counterparts.  

Could it be possible that due to socialization, biology or another cause, women are actually underperforming?

Nope. Researchers found that men ranked other men above women with equal or better GPAs. In fact, they ranked men three-quarters of a GPA point above women with the exact same grades. 

Could it be that male students assert themselves more confidently, and therefore come off smarter?

Probably not. Researchers asked instructors which students were most outspoken, and while they were more likely to name men, that didn't account for the difference in ratings. Even the most outspoken women were ranked more than three-quarters of a GPA point below their male peers.

"Using UW's standard grade scale, that's like believing a male with a B and a female with an A have the same ability," lead author Sarah Eddy said in a press release.

These findings further debunk the prevalent stereotype that women are lagging behind in STEM fields.

"The observed bias in males means they may not be supporting a female peer to the extent they should given her actual ability in the class," Eddy told NTRSCTN in a statement. "This lack of support could impact her belief that she is actually competent in biology and through that her persistence."  

Previous studies have found that professors grade female students based on looks, students give better evaluations to online professors with male names, and professors are less likely to hire a lab manager with a female name. 

Hopefully, these studies help people understand that science's gender gap has a lot more to do with biased towards women than it does with their abilities.