Of those 405 women included in the sample, 6.4 percent — or 26 women — reported a pregnancy that year. A separate large-scale study showed that, for the general population of women that age, the per-incidence pregnancy rate for a single act of intercourse is 3.1 percent.
As to why rape victims would have a higher rate of pregnancy, the Gottschalls put forward a few theories. They look at previous research, which suggests that men are more attracted to women who are fertile and ovulating. In consensual sex, women can decline sex at a time where there might be a high likelihood of pregnancy. That's not the case in rape.
"Rapists do not wait to be chosen, rapists choose," they write. "As such, within the limits of opportunity, rapists would be able to target women bearing cues [of fertility]."
The Gottschalls do acknowledge that their study was at odds with previous research, which showed a lower rate of pregnancy among rape victims.