Although the IWF doesn’t say what the purpose of presenting this statistic is, most readers will take it as an indication of how outrageously high Koss’ numbers are. (Indeed, if that isn’t the point, why on earth include the statistic in a critique of Koss at all?)
Such a comparison is wildly unscientific and irresponsible. No legitimate comparisons can be made between a lifetime prevalence self-report survey and the numbers of such incidents that occur on campus in one year. But for the purpose of rebutting the IWF’s bad methodology, I’m going to pretend they can be compared. And unlike the IWF, I’m going to do the math. How far apart are this stat and the numbers given in Koss’ report?
To start with, we need to ask “how many female undergraduates are on an average college campus?” (Koss’ statistic about rape victims included only female undergrads). According to The Chronicle of Higher Education, in 2000 there were 12,450,587 undergrads in the USA. Of those, 55.9%, or 6,959,878, were women. There are 4,096 colleges and universities in the US, which works out to an average of 1,699 female undergrads per college campus.
So of those 1,699 women on a college campus, how many will be victims of rape in a typical year, according to Koss’ numbers? The famous “1 in 4″ figure is a lifetime figure that includes both rape and attempted rape; the “less than one per campus” figure, on the other hand, is about completed rapes within a single year. So we can’t compare those two numbers directly.
Fortunately, Koss’ report includes a calculation of annual incidence of completed rapes only – out of 3,187 undergraduate women Koss surveyed, 207, or 6%, were victims of rape in the past year. Since the average US campus has 1,699 female undergrads, and 6% of 1,699 is 102, according to Koss’ study we’d expect 102 undergraduate women at an average college to be victims of rape each year.
Look again at the statistic the anonymous IWF author is comparing Koss to: “…campus police reported 1,310 forcible sex offenses on U.S. campuses in one year.” So we’re not talking about all the rapes that happen in a single year; just the rapes that happen “on U.S. campuses.”
Koss’ survey asked rape victims if the rape had taken place on or off campus. 14% reported that it had taken place on campus. So out of 102 rapes happening to undergraduate women in a year, according to Koss’ results, we’d expect 15 to actually take place on campus.
But we can’t assume that all 15 reported the incident to campus police. According to Koss, only 5% of rape victims said they had reported the incident to the cops at all. And 5% of 15 is 0.75.
So according to the statistic the IWF offers – a statistic that, clearly, is meant to discredit Koss’ results – there is “an average of fewer than one rape per campus” per year that campus police know about. And according to my calculations, based on Koss’ numbers we’d expect to see – less than one rape known to the cops per college campus per year.
In other words, Koss’ study found exactly what it should have, according to the statistic the IWF author supplied. So how, exactly, does that disprove Koss?