The point isn't to vie for the distinction of being the worst off, of course, but to get a more accurate understanding of poverty so we might make a little more headway on getting rid of it. The single mom narrative—specifically the idea that having a child out of wedlock causes poverty—has stubbornly held on to the public imagination since the days of Murphy Brown and before.

Brown, you may remember, was the fictional news anchor at the heart of her own sitcom who became the cautionary poster-mother for conservatives when she had a child on her own. No doubt part of the hubbub back then was a reaction to the fact that family structure was changing. But that was in the early '90s, when, for the first time in our nation's history, more than a quarter of mothers were single (compared with five percent 30 years earlier) and Murphy was sporting a Farrah-do and suits with shoulder pads.

Today, the number of unmarried mothers is holding fairly steady. And more of those mothers are working as women's employment has increased over the years. Even more important, the notion that being a single mother leads to poverty—as opposed to the other way around—has been debunked, or at least be proven to be way more complicated than that. Kathryn Edin, a professor of public policy at Harvard, provides perhaps the best exploration of the relationship between poverty and single motherhood in Promises I Can Keep, her book on the myriad reasons that poor women put motherhood before marriage.

Yet, the single mom storyline still drives some of the responses to poverty, including marriage promotion programs, which were begun under President George W. Bush and continue, though in a diminished way, under Obama. The new data on poor married parents is evidence that a more nuanced response is in order.

"Poverty and economic insecurity are about a lot more than having children out of wedlock," says Fremstad, who notes that many of the people now viewed as "single" in poverty statistics actually live with a partner. "There are a lot of people who, if they said 'I do,' would still be in the same boat." Fremstad also says that the data show disability is also a significant problem, affecting roughly 10 percent of poor married families

But the biggest lesson from the emergence of the married poor is that parents don't just need jobs, they need good jobs. Without a decent wage, some flexibility, and paid time off to take care of family members, just saying "I do" clearly isn't enough to keep anyone out of poverty.