If you ask President Obama what portion of female college students are raped, he’ll tell you the number is one out of every five. If you ask critics of the current movement to combat campus sexual assault, they’ll tell you that widely quoted figure is hugely unreliable.

Today we have one more piece of data, and it largely backs up the president.

A new study, published this week in the Journal of Adolescent Health, finds that 15.3% of female students at one New York college were subjected to rape or attempted rape in their freshman year. If you expand the scope of the question to include the following summer, the figure jumps to 18.9%.

So what’s behind these numbers? The study, which defined sexual assault more narrowly than some others have, looked at two categories of rape — assaults committed through force or the threat of force, and assaults committed while the victim was incapacitated by drugs or alcohol. The authors found that 7.3% of women surveyed experienced at least one attempted or completed forcible rape in their first academic year, while 12.1% experienced attempted or completed rape by incapacitation.

Does the 15.3% figure for the first year suggest that the one-in-five number is actually too low? Maybe not. This is only one college, remember, and these kinds of statistics are never precise. Other studies have found that sexual assault is most common during the early stages of college, and this report backs that up — the authors found a twenty-five percent drop in the number of students experiencing sexual violence from the fall semester to the spring.

More troublingly, the authors also found that many women in the study were subjected to more than one sexual assault in their first year. Although they didn’t break out those numbers directly, it’s plain from their data that many of those assaulted in the spring (and the summer) had been assaulted in the fall as well.

The study asked about sexual assault earlier in life, and found that it was widespread as well — some 28% of women in the survey said they had experienced rape or attempted rape between their fourteenth birthday and enrollment in college. (Most of these sexual assaults seem to have been attempted, though the study doesn’t provide that analysis explicitly.)

One of the study’s most chilling findings is the extent to which previous sexual assault — particularly sexual assault by incapacitation — predicted future assaults. Forty-one percent of the women who reported rape or attempted rape by incapacitation before college reported the same experience in their first collegiate year, compared to just ten percent of those who had not been subjected to sexual assault by incapacitation in high school. For rape by force in college, there was a similar gap between those who had experienced assault by incapacitation before and those who had not — twenty-three percent versus six percent.

The authors don’t attempt to explain the cause of this gap, which is seen again (though to a much smaller extent) among women who had experienced forcible sexual assault before college. Different observers will interpret the data in different ways — a fact which underscores the importance of this study and our desperate need for more data in this area.

Critics of anti-rape activism frequently highlight gaps and contradictions in our statistical understanding of sexual assault as cause for skepticism or mockery. It’s true that there’s a lot that we still don’t know, and that relying too heavily on any one statistic is dangerous. Does this study prove that one in five college women will experience rape? It doesn’t. That’s information we still don’t have.

But what this study, and studies like it, do accomplish is moving us toward a better understanding of the scope and nature of our society’s sexual assault crisis.

We know that by even the most conservative estimates, hundreds of thousands of women are sexually assaulted in the United States each year. We know that a significant — and disproportionate — number of those rapes and attempted rapes take place on campus.

But we don’t actually know much for sure beyond that. Anyone who tells you with any specificity how frequently sexual assault occurs in our colleges or in our society is lying, or guessing. But that fact is itself damning — a reflection of how long we ignored rape in this country, and how early we are in our efforts to come to grips with it.

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Note: Most of the figures in this piece are taken from the full JAH study, which is not currently available to the general public online.