Married men do less housework than live-in boyfriends, finds an international survey.

But married women do more housework than their live-in counterparts.

“Marriage as an institution seems to have a traditionalizing effect on couples—even couples who see men and women as equal,” said co-researcher Shannon Davis, a sociologist at George Mason University in Virginia.

Understanding the dynamics of couples who live together but are not married has become more important as cohabitation around the globe increases. More than 5 million unmarried partner households (more than 10 million individuals) currently exist in the United States, according to a 2006 report by the U.S. Census Bureau.

"I do," just not housework

The scientists analyzed surveys gathered in 2002 from 28 nations, from 17,636 respondents (8,119 males and 9,517 females) as part of the Family and Changing Gender Roles III Survey. All respondents were either married or cohabiting with a significant other.

Overall, they found men spent about 9 hours a week on housework compared with women, who spent more than 20 hours weekly.

"There's still a gender norm, since women do more housework than men regardless of union type," said study team member Jennifer Gerteisen Marks, who is working on a doctorate degree at North Carolina State University.

Regardless of the couples' relative earnings or work hours, cohabiting males reported more household hours than did their married counterparts, while the opposite was true for women, with wives picking up the broom more often than live-in girlfriends.

Equal partners

Other factors also came into play. Men who raked in more earnings than their partners did fewer hours of housework than men with lower relative incomes. "Those in the household with greater resources will leverage those resources to bargain their way out of housework," the authors write in the September issue of the Journal of Family Issues.

Couples who viewed men and women as equals were more likely to divvy up chores equally. But even in "egalitarian households," married men still contributed less to household chores than did their wives.

"It's consistent with prior research, which has shown that the roles of wives and husbands are very powerful," Marks told LiveScience. "In a cohabiting relationship there aren't such strongly prescribed social norms, which trickle down to things like housework."