Here's a Vox article I read today which discusses multiple surveys concluding roughly 1 in 5 women in college will be sexually assaulted by graduation. It also mentions that the Bureau of Justice Statistics' National Crime Victimization Survey estimates the number at 1 in 40 (but that that survey has "even more problems").

Could anyone explain why these rates are so different? I understand that a lot has to do with what each survey defines as "sexual assault" but one yields numbers that differ by an order of magnitude. It seems like there must be something which is either heavily inflating one statistic or heavily suppressing the other (or some combination of the two).

Has anyone looked into this who could give some good examples of what is being classified as sexual assault in one but not the other?