4 in 10 households in America have mothers as the principal breadwinner, compared to about 1 in 10 in 1960. The data, as reported by Pew Research, shows that two groups of women are driving this trend from opposite sides of the economic spectrum.

The study looks at moms who are either the sole or primary source of income for their families.

“[In] one group, the mothers are married and they make more money than their husbands,” says Wendy Wang, lead author of the study.

Married women were breadwinners in 15 percent of the households surveyed in 2011. In 1960, that number was 4 percent.

“They’re more educated than their husbands and their family income is about $80,000 a year,” Wang says.

Contrast that to the second group: Single moms. They’re breadwinners for a 25 percent of families in the U.S., up from 7 percent in 1960.

And yet, “for single mothers the median income was only about $23,000,” Wang says. That’s less than half of national median family income. Wang says there’s no clear cut storyline here.

While married breadwinning moms out-earn their male counterparts. More single moms are leading households and that means more families are slipping into poverty.