In a trend accelerated by the recent recession and an increase in births to single mothers, nearly 4 in 10 families with children under the age of 18 are now headed by women who are the sole or primary breadwinners for their families, according to a report released Wednesday by the Pew Research Center.

The report reveals a sweeping change in traditional gender roles and family life over a few short decades: The number of married mothers who out-earn their husbands has quadrupled, from 4 percent in 1960 to 15 percent in 2011. Single mothers, who are sole providers for their families, have tripled in number, from 7 to 25 percent in the same period.

"The decade of the 2000s witnessed the most rapid change in the percentage of married mothers earning more than their husbands of any decade since 1960," said Philip Cohen, a University of Maryland sociologist who studies gender and family trends. "This reflects the larger job losses experienced by men at the beginning of the Great Recession. Also, some women decided to work more hours or seek better jobs in response to their husbands' job loss, potential loss or declining wages."