At 12.9 percent, Philadelphia has the highest rate of deep poverty — people with incomes below half of the poverty line — of any of the nation's 10 most populous cities. The numbers come from an examination of 2009-11 data from the U.S. Census American Community Survey by the Inquirer and Temple sociologist David Elesh. While many people who live just below the poverty line often move out of poverty, those in deep poverty are in such a profoundly disadvantaged state that they're more likely to stay mired in it, according to Judith Levine, a Temple sociologist. "Poverty becomes a long-term experience, and it's very different, especially for children," she said.