A group of researchers from the University of California San Francisco looked across the top 50 U.S. med schools, and found that men with facial hair made up 19% of clinical department heads, while women accounted for only 13%.

The study, which was published Wednesday in the British Medical Journal, is a quirky one, and the researchers came up with a so-called “mustache index” as part of the analysis. The index compares the proportion of women to the proportion of mustaches in department head positions using “multinomial logistic regression models.” An index of 1 means an equal proportion of women and mustaches. The mustache index for top 50 U.S. med schools is 0.72, which means that there are about 0.72 women for every man with a mustache in a top position at one of these schools.

Though a “mustache index” sounds slightly ridiculous, the study highlights a serious issue: the yawning the gender gap in medicine. After all, how many men with mustaches do you know? (According to the study, less than 15% of American men have them.) And the gap has nothing to do with women’s desire to become doctors: Over the past 15 years, almost half of medical students have been women. However, as you look higher up the academic ranks, the so-called “pipeline problem” kicks in. Just women account for just 38% of full-time medical faculty members, 21% of full professors, and 16% of deans.

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