It’s no secret that single motherhood is a prescription for economic insecurity for many women.

Single-mother families are nearly five times as likely to be poor than married-couple families and a majority of America’s poor children live in single mother-led households, according to the left-leaning Center for American Progress.

At the other end of the political spectrum, the conservative Heritage Foundation says marriage is the greatest weapon against child poverty.

“Family disintegration, lack of education, and counterproductive welfare incentives all contribute to child poverty,” Heritage wrote recently. “Rebuilding a strong marriage culture should be at the forefront of our efforts to fight poverty.”

A New York Times story cited a number of studies that attributed the growing income gaps in American society to the changing structure of the typical family with the growing number of single parent families. The article suggested that changing marriage patterns could account for anywhere from 15-40% of growing income inequality across the country, with a surge in births outside of marriage among less educated women pushing single-parent families into the lower end of the socio-economic range.

“College-educated Americans … are increasingly likely to marry one another, compounding their growing advantages in pay,” The Times said. “Less-educated women…are growing less likely to marry at all, raising children on pinched paychecks that come in ones, not twos.”

“It is the privileged Americans who are marrying, and marrying helps them stay privileged,” said Andrew Cherlin from Johns Hopkins University.

Now there’s even more evidence connecting single-motherhood to poverty.

The Earned Income Tax Credit (EITC) is a refundable tax credit for low to moderate income working persons, particularly those with children.

The Brookings Institution, a Washington, D.C.-based centrist think tank, put together an illuminating interactive map of the share of taxpayers that claim the EITC at the county level nationwide:

Map: The Earned Income Tax Credit in Your County

Brookings then compared the EITC map with a map of single motherhood in the United States in the most recent year for which complete data is available.

Map: Percent of all households that are single female headed with children in 2010.

The principal conclusion? The map of EITC benefits by county looks a lot like a map of single motherhood.

As Brookings points out, looking at the number of parents in a household as an indicator of financial stability and opportunity, changing marriage patterns could account for anywhere from 15-40% of growing income inequality across the country.

While correlation doesn’t necessarily equal causation, the link between poverty and mothers with children growing up without a father is clearly something that ought to be part of the discussion of income inequality in the United States.