From Huffington Post:

At the end of a largely wonky, data-driven piece of analysis written for Bloomberg News, Krueger discounted the incessant focus on the unemployment rate -- which does not count jobless people who have grown so discouraged that they have given up looking for work -- arguing that the real action is found in the so-called employment-to-population ratio, which measures what slice of working age Americans are employed. The ratio then sat at a dismal 58.4 percent, just off the low reached the previous December, meaning that the supposed resumption of economic growth was not putting large numbers of jobless people back to work.

Even back when the economy was still technically expanding between 2002 and 2007, Krueger noted, the percentage of working age people then employed never got back to where it had been before the previous recession in 2001, at a peak of 64.7 percent. More here.