Rep. Todd Akin caused a public outcry Sunday when he suggested that women who were "legitimately raped" would rarely become pregnant. Study after study has proven that theory false. But one provocative study, published in 2003, went even further: It found that a single act of rape was more than twice as likely to result in pregnancy than an act of consensual sex.

The study, "Are per-incident rape-pregnancy rates higher than per-incident consensual pregnancy rates?" was published in the journal Human Nature by Jonathan A. Gottschall and Tiffani A. Gottschall, two professors at St. Lawrence University in Canton, N.Y. They used data from the federally administered National Violence Against Women survey. There, they found a sample of 405 women between the ages of 12 and 45 who had experienced one incidence of rape that included intercourse.

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.