Think women can’t do math? You’re wrong – but new research shows you might not change your mind, even if you get evidence to the contrary. A study of how both men and women perceive each other’s mathematical ability finds that an unconscious bias against women could be skewing hiring decisions, widening the gender gap in mathematical professions like engineering.

The inspiration for the experiment was a 2008 study published in Science that analyzed the results of a standardized test of math and verbal abilities taken by 15-year-olds around the world. The results challenged the pernicious stereotype that females are biologically inferior at mathematics. Although the female test-takers lagged behind males on the math portion of the test, the size of the gap closely tracked the degree of gender inequality in their countries, shrinking to nearly zero in emancipated countries like Sweden and Norway.

That suggests that cultural biases rather than biology may be the better explanation for the math gender gap.

To tease out the mechanism of discrimination, two of the authors of the 2008 study, Paola Sapienza and Luigi Zingales, economic researchers at Northwestern University’s Kellogg School of Management in Evanston, Illinois, and the University of Chicago Booth School of Business in Illinois, respectively, teamed up with Ernesto Reuben, an experimental psychologist at Columbia Business School in New York City, to design an experiment to test people’s gender bias when it comes to judging mathematical ability.

Study participants of both genders were divided into two groups: employers and job candidates.

The job was simple: As accurately and quickly as possible, add up sets of two-digit numbers in a 4-minute math sprint. (The researchers did not tell the subjects, but it is already known that men and women perform equally well on this task.)

At the end of the experiment, the employers took the Implicit Association Test, which measures unconscious bias by forcing you to quickly group together various words. If you associate the word “man” with the word “math” more quickly than “woman” and “math,” for example, that reveals a possible bias.