It’s all bullshit.
RAINN says the numbers are 1/6, although those are based on reported numbers and I believe the actual count to be closer to 1/4 and 1/3 when unreported rapes are taken into account. These statistics also do not take into account victims/survivors of repeated rape and sexual assault by one perp or more than one perp. Keep that in mind.
The CDC (Centre for Disease Control) says 1/5 in this .pdf, again I believe the numbers to be higher for both female and male victims/survivors of rape and again those victims/survivors of multiple and repeated rape by one perp or one than one perp are not taken into account.
Both of the above are US based stats I believe.
The Girls Action Foundation’s Beyond Appearances: Brief on the Main Issues Facing Girls in Canada .pdf has information pertaining to statistics based in Canada. While there is no overall “rape rate” for female people reported, this report is focused on girls and young women and provides statistics related to sexual harassment rates, radicalized violence and mental health issues among many other female experiences. I specifically reference this brief because it was used for lecture in an Applied Social Psychology course I took in uni.
More .pdfs useful by the Girls Action Foundation can be found here.
The World’s Women Trends and Statistics .pdf put out by the UN in 2010 cites the rate of sexual violence ranging for women worldwide, anywhere from numbers as low as 5% of the population to numbers as high as 50%.
Again this is only based on reported statistics, which have issues I raised above. As well, the country-specific rates will be affected by how specific cultures value female victims/survivors of sexual violence, how sexual violence is defined in the specific culture, how willing women are to disclose being victims/survivors of sexual violence, how dangerous is it is to disclose, etc.
Another UN resource, Ending violence against women: From words to action. Study of the Secretary-General (publication version .pdf) has information regarding country-specific statistics starting on page 48. More .pdfs specifically from the UN can be found on this page.
If anyone wants to add more country-specific statistics originating from organizations other than the UN, please feel free to edit (mods) or reblog (followers) and I will reblog here for more information.
I hope this helps.