The latest U.S. Census stats show that women make up only about a quarter of the workforce in the science, technology, engineering and math fields today. But why? A new study published in PLOS ONE and reported by Mother Jones may help explain one ugly possibility: The majority of women who work in research said they’ve faced sexual harassment while conducting scientific fieldwork.

For the study, researchers took stats from an online survey of 516 women and 142 men in various scientific fields, including archaeology, anthropology and biology that asked specifically if they’d suffered sexual misconduct in their field.

Astonishingly, the majority—or, 64 percent—of female researchers said they had been sexually harassed while working at a field site. What’s more, one in five women said they had been victims of sexual assault in this setting.

Delving deeper, the survey showed that the perpetrators of sexual misconduct against most of these women were their direct supervisors. In addition, at the time of the incidents, 90 percent of the female scientists who were harassed or assaulted were young undergraduates, post-graduates or post-doctoral students.

“We worry this is at least one mechanism driving women from science,” said Kate Clancy, PhD, an assistant professor of biological anthropology at the University of Illinois, and lead author of the study. (The report added that many university science programs require students to complete fieldwork and that students who do so are much more likely to receive highly competitive research grants.) The survey data was published just as Congress began a huge investigation on how American college campuses respond to sexual harassment and assault allegations. Many women develop debilitating post-traumatic stress disorder, depression and anxiety symptoms after a sexual assault.