WASHINGTON (MarketWatch)—Among the U.S. poor, women and Southerners are likely to endure some of the longest spells of poverty, according to government data released Thursday.

Up to 15% of Americans live in poverty, and for some groups the hardship can run on. The median length of a poverty spell among Americans was 6.2 months—a period that extended to 6.6 months for women, the U.S. Census Bureau reported for a period covering 2009 through 2012.

“Just as women are more likely to be poor than men, they are also likely to be poor for longer…Women tend to be deeper in poverty than are men,” said Katherine Gallagher Robbins, a senior policy analyst at the National Women’s Law Center, a Washington-based advocacy group. “Insofar as women in poverty are more likely to have children than men in poverty, it takes more money to pull these women above the poverty line.”

About 16% of women were in poverty last year, compared with 13% of men, according to a government report. Households run by women in which a husband wasn’t present had the lowest income in 2013, at about $35,000—that’s 46% of the income for married-couple households. Meanwhile, households maintained by men in which there was no wife had income of about $51,000.

By region, Southerners had the longest spells of poverty, with the median hitting 7.1 months, compared with 6.2 months in the Northeast, 5.8 months in the Midwest and 5.1 months in the West. The 2013 poverty rate was the highest in the South, hitting 16%, while the rate in the West was almost 15%, and the rate in both the Northeast and the Midwest approached 13%.

Regional differences are due, in part, to the relative strength of local labor markets, wages and economic opportunities, experts said. Recent research from economists at Harvard and the University of California, Berkeley, found that there’s low income mobility in the South, except for Texas. Southern children have a relatively low chance of moving up the income distribution.

“The U.S. is often hailed as the ‘land of opportunity,’ a society in which a child’s chances of success depend little on his family background,” the authors wrote. “The U.S. is better described as a collection of societies, some of which are ‘lands of opportunity’ with high rates of mobility across generations, and others in which few children escape poverty.”

Others groups with extended poverty spells were people at least 65-years old, Americans without a high-school diploma, African-Americans, and those who were separated, divorced or widowed. The median poverty spell for each of these groups was at least eight months.

There’s persistent and finite poverty in the U.S. Among those in poverty from 2008 through 2009, about 5% were in poverty for that entire period, according to the Economic Policy Institute, a left leaning Washington think tank. Low-wage employment and slow income growth for those with earning at the bottom of the scale are major factors behind poverty. Also, medical emergencies and other shocks can damage a family’s personal finances.