If you read the BJC report:

http://www.bjs.gov/content/pub/pdf/rsavcaf9513.pdf

you'll also note that the follow-up interviews also estimate that 80% of sexual assaults in college-age female students are not reported to law enforcement. I think whether it is an over or underestimate (and my bias is in the under direction), it is clear that we do not have a good research or societal handle on either the behavior or its prevalence.

...pronounced like the long vowel and first letter of the alphabet...