Left-handed men who attended at least a year in college go on to earn significantly more than their right-handed classmates – even more reason they’ll be celebrating International Left-Handers Day today.

“Among the college-educated men in our sample, those who report being left-handed earn 13 percent more than those who report being right-handed,” said economist Christopher Ruebeck of Lafayette College. Ruebeck and his research partners, Joseph Harrington Jr. and Robert Moffitt of Johns Hopkins University, reported the findings in a new working paper published by the National Bureau of Economic Research.

And lefties, stay in school: Those who finished all four years of college earned, on average, a whopping 21 percent more than similarly educated right-handed men. Curiously, the researchers found no wage differential among left- and right-handed women.

They based their conclusions on an analysis of data from the federally funded National Longitudinal Survey of Youth, a nationally representative survey of approximately 5,000 men and women first interviewed in 1979, when they were 14 to 21 years old. Their analyses was based on the 1993 follow-up survey, when respondents were 28 to 35. Left-handers made up about 10 percent of their sample and the population as a whole.

While evidence of a wage gap was unequivocal, explanations for the disparity proved more elusive. Differences in biology and brain function are two possibilities. Nor do the researchers know why they didn’t see a similar effect among women.

“We do not have a theory that reconciles all of these findings,” they admit.

The study is the latest to suggest there’s something special about lefties. Other researchers have found that left-handers are overrepresented on university faculties, as well as among gifted students, artists and musicians.