Mobility as an economic measure

Many Americans believe that ours is a very economically mobile society, a country where we can still pull ourselves up by our bootstraps. But that's not true.

"Contrary to that common belief, by most measures of mobility, the United States has some of the lowest measures of upward-mobility of any developed country in the world," said Nathaniel Hendren, a professor of economics at Harvard University.

Hendren said the odds that an American kid who is born into the bottom 20 percent of the income scale will make it to the top 20 percent are very low, around seven percent. What's more, he said, the odds of going from rags-to-riches in the U.S. have always been fairly low. A shrinking middle class could make mobility even more rare.

"When you look across areas within the United States, areas with stronger middle classes tend to have higher rates of upward mobility," Hendren said. 

Erin Currier, director of the Financial Security and Mobility Project at the Pew Charitable Trust, said mobility researchers have identified a phenomenon they call "stickiness at the ends."

"Families who are raised at the bottom of the income distribution or the very top of the income distribution are highly likely to stay there," Currier said.

Members of the middle class are more likely to evade that stickiness, and to move around the income spectrum over time. 

"People who are raised by solidly middle-income families actually have the most economic mobility, both up and down," Currier said. "They are equally likely to stay in the middle, move to the top, or move to the bottom."

Moving to the top of the spectrum isn't cause for concern, but those who move to the bottom and get stuck are more like to find their children stuck there as well.