I was referring specifically to a study done by two University of Victoria students. It was in no way a representative sample. That was the result of their study.
As I said, we don't have data, but based on my experience and the job advertisements that we've looked at and the interns I've spoken to, it's my belief that the vast majority of unpaid interns are women. It's also because the industries that are most likely to do unpaid internships—journalism, nutrition, social work, marketing, public relations—are all female-dominated areas.