According to an over 100 page federally-funded study The Campus Sexual Assault (CSA) Study, studying the January 2005 through December 2007 time period:
Nearly 5% of the total sample was forcibly sexually assaulted since college entry (4.7%, box 9). More than three percent of the women (3.4%) experienced forced rape since entering college (box 11) and 1.4% experienced forced sexual battery since entering college (box 10). Approximately 11% of the women experienced sexual assault while incapacitated since entering college (box 12), with a higher percentage of women being victims of incapacitated rape than incapacitated sexual battery since entering college (8.5%, box 14 compared to 2.6%, box 13, respectively).
In this study, "rape" was defined as:
sexual assault that entailed oral, vaginal, or anal penetration
It should be kept in mind that this study is done upon women 18-25 who are full time enrolled in college. In other words, there are freshmen, sophomores, juniors and seniors. However, the study finds that it is mostly as freshman and sophomores that college woman are sexually assaulted. Restricting the data to only seniors (who are the only ones approaching a complete college experience):
6.9% of seniors were victims of physically forced sexual assault since entering college, and 16% of seniors were victims of incapacitated sexual assault since entering college.
ConsideringWhile not in the aboveoriginal publication of the report, as pointed out by user=pericles316, two of the "1authors of the report released the following additional information in 5" statistic is reasonably supported by this studythe article Setting the Record Straight on ‘1 in 5’:
The number of what college womenfemale seniors in the survey who reported being raped was 14.3%.
This is about 1 in 7 self-reportreporting being raped during college. Considering that the data was collected during the winter, the seniors still had one semester of college left, so 1 in 6 is a reasonable overall estimate, but 1 in 5 is too high.