There's the "official" unemployment rate, based on claims for unemployment benefits - and the more accurate U-6, which looks at discouraged workers who have stopped looking:

They were left out of the latest unemployment rate, as they are every month: millions of hidden casualties of the Great Recession who are not counted in the rate because they have stopped looking for work.

But that does not mean these discouraged Americans do not want to be employed. As interviews with several of them demonstrate, many desperately long for a job, but their inability to find one has made them perhaps the ultimate embodiment of pessimism as this recession wears on.

Some have halted their job searches out of sheer frustration. Others have decided it makes more sense to become stay-at-home fathers or mothers, or to go back to school, until the job market improves. Still others have chosen to retire for now and have begun collecting Social Security or disability benefits, for which claims have surged.

[...] The official jobless rate, which garners the bulk of attention from politicians and the public, was reported on Friday to have risen to 9.7 percent in August. But to be included in that measure, which is calculated by the Bureau of Labor Statistics from a monthly nationwide survey, a worker must have actively looked for a job at some point in the preceding four weeks.

For an increasing number of people in this country who would prefer to be working, that is not the case.

It is difficult to assign an exact figure, because of limitations in the data collected by the bureau, but various measures that capture discouragement have swelled in this recession.

In the most direct measure of job market hopelessness, the bureau has a narrow definition of a group it classifies as “discouraged workers.” These are people who have looked for work at some point in the past year but have not looked in the last four weeks because they believe that no jobs are available or that they would not qualify, among other reasons. In August, there were roughly 758,000 discouraged workers nationally, compared with 349,000 in November 2007, the month before the recession officially began.

The bureau also has a broader category of jobless it calls “marginally attached to the labor force,” which includes discouraged workers as well as those who have stopped looking because of other reasons, like school, family responsibilities or health issues. But economists agree that many of these workers probably would have found a way to work in a good economy.