http://www.bmj.com/content/351/bmj.h6311
"We want to increase the representation of women in academic medical leadership by drawing attention to sex disparities. We compared the proportion of women in leadership positions with the proportion of individuals with moustaches. We chose to study moustaches as the comparator because they are rare (<15% of men from the most recent measures available), and we wanted to learn if women were even rarer. Our hypothesis was that fewer women lead academic medical departments in the US than individuals with moustaches."