With Justice Ruth Bader Ginsburg – who’s battled cancer twice now – currently serving as the Supreme Court’s only female justice, it’s no surprise that many have predicted President Obama will choose a female nominee for David Souter’s soon-to-be vacant seat.

There are plenty of reasons to have another woman on the court (among them: the majority of the United States population is female; one-third of U.S. attorneys are women; and about 30% of judges on the lower federal courts are female). However, male or female, many news stories have forecast that the replacement of left-leaning Souter won’t have a significant difference in the high court’s decisions.

Well, here’s a twist, a research discovery that I found fascinating from Sunday’s Outlook section of The Washington Post (yes, even Web editors read the print edition from time to time).

Researchers from Washington University in St. Louis and Northwestern University School of Law studied the votes of federal court of appeals judges in many practice areas. They presented their findings in an award-winning paper, Untangling the Causal Effects of Sex on Judging (PDF).

They found no significant difference in the voting patterns of male and female judges on the majority of areas. The notable exception is not terribly surprising: in sex discrimination cases, female judges are about 10% more likely to rule in favor of the plaintiff bringing the claim.

Here’s what was surprising, at least to me: the presence of a female judge changes the way male judges vote.

They write: “When male and female judges serve together to decide a sex discrimination case, the male judges are nearly 15 percent more likely to rule in favor of the party alleging discrimination than when they sit with male judges only.”

So, to sum: ‘Out of sight, out of mind’?

The piece from WaPo concludes: “The retirement of the liberal-leaning Souter may not give the president a chance to move the court significantly to the left. But it does let him make a different shift. If he does choose a woman to fill Souter’s seat, he could have a major impact on an area of law that’s important to many Americans — women and men alike.”