While the campaigns eagerly pursue female voters, there's something that may raise the chances for both presidential candidates that's totally out of their control: women's ovulation cycles.
You read that right. New research suggest that hormones may influence female voting choices differently, depending on whether a woman is single or in a committed relationship.
Please continue reading with caution. Although the study will be published in the peer-reviewed journal Psychological Science, several political scientists who read the study have expressed skepticism about its conclusions.
A bit of background: Women are more likely to vote than men, other studies have found. Current data suggest married women favor Gov. Mitt Romney, in a 19% difference, over President Barack Obama, while Obama commands the votes of single women by a 33% margin, according to the study. And previous studies have shown that political and religious attitudes may be influenced by reproductive goals.
In the new study's first experiment, Kristina Durante of the University of Texas, San Antonio and colleagues conducted an internet survey of 275 women who were not taking hormonal contraception and had regular menstrual cycles. About 55% were in committed relationships, including marriage.
They found that women at their most fertile times of the month were less likely to be religious if they were single, and more likely to be religious if they were in committed relationships.
Now for the even more controversial part: 502 women, also with regular periods and not taking hormonal contraception, were surveyed on voting preferences and a variety of political issues.
The researchers found that during the fertile time of the month, when levels of the hormone estrogen are high, single women appeared more likely to vote for Obama and committed women appeared more likely to vote for Romney, by a margin of at least 20%, Durante said. This seems to be the driver behind the researchers' overall observation that single women were inclined toward Obama and committed women leaned toward Romney.
Here's how Durante explains this: When women are ovulating, they "feel sexier," and therefore lean more toward liberal attitudes on abortion and marriage equality. Married women have the same hormones firing, but tend to take the opposite viewpoint on these issues, she says.
"I think they're overcompensating for the increase of the hormones motivating them to have sex with other men," she said. It's a way of convincing themselves that they're not the type to give in to such sexual urges, she said.
Durante's previous research found that women's ovulation cycles also influence their shopping habits, buying sexier clothes during their most fertile phase.
"We still have the ovulatory hormones that have the same impact on female brains as across other species," she said. We want sex and we want it with the best mate we can get. "But there are some high costs that come with it," she said, particularly for women who are already in committed relationships.
This isn't the first time hormones have been looked at in connection to voting. Last year Israeli researchers published a study in the journal European Neuropsychopharmacology examined the stress hormone cortisol in voters in Israel. Levels of this hormone were higher in people right before they were about to vote than in the same people when they were not voting.
Durante's study on women noted that liberal attitudes favor social equality and tend to be less associated with organized religion. Conservatism is more about traditional values and is linked to greater participation in organized religion.
The most controversial part of the study is not only that hormonal cycles are linked to women's preferences for candidates and voting behaviors, but also that single women who are ovulating are more likely to be socially liberal, and relationship-committed women are more likely to be socially conservative, said Paul Kellstedt, associate professor of political science at Texas A&M University.
One of the major caveats this paper fails to address is that men also have biochemical changes, Kellstedt said.
"The reader may be left with the impression that women are unstable and moody in ways that extend to their political preferences, but that men are comparative Rocks of Gibraltar," Kellstedt said in an e-mail.
Kellstedt does not study biology, but he has been involved in research suggesting that men's political preferences are even more volatile than women's.
"There is absolutely no reason to expect that women's hormones affect how they vote any more than there is a reason to suggest that variations in testosterone levels are responsible for variations in the debate performances of Obama and Romney,"
said Susan Carroll, professor of political science and women's and gender studies at Rutgers University, in an e-mail.
Carroll sees the research as following in the tradition of the "long and troubling history of using women's hormones as an excuse to exclude them from politics and other societal opportunities."
"It was long thought that a woman shouldn't be president of the U.S. because, God forbid, an international crisis might happen during her period!" Carroll said.
A better explanation for the divide in voting preferences between single and married women is the difference in economic status, she said.
One expert gave it a little more credence: Israel Waismel-Manor, a political scientist at the University of Haifa in Israel, who did the cortisol study last year.
He's not sure that this hormonal effect Durante found among women isn't real, but offered an alternate explanation too: Research has shown women prefer more "manly men" when they are in their most fertile phases of the cycle. Obama and Romney are both handsome, in good physical shape and could fit the type of "provider of the family," so either could fit the ideal, depending on a woman's preference.
Assuming there is some hormonal explanation, the effects could cancel themselves out, since different women will be on different cycles when they vote, and the candidates have a similar level of physical attractiveness, Waismel-Manor said. A more elaborate research design is needed to examine it further.
"Even if the finding is correct, there's a chance that it won't have a cumulative effect on the electorate," he said.