When Daniel McCune graduated from college three years ago, he was optimistic his good grades would earn him a job as an intelligence analyst with the government.
With a Bachelor of Science degree from Liberty University in Virginia, majoring in government service and history, McCune applied for jobs at the National Security Agency, the Federal Bureau of Investigation and other agencies.
But after a long hunt that yielded only two interviews, the 26-year-old threw in the towel last fall, joining millions of frustrated Americans who have given up looking for work.
"There's nothing out there and there probably won't be anything for a while," said McCune, from New Concord, Ohio. He has moved back home to live with his parents, who are helping him pay off his college debt of about $20,000.
"I don't like it, it's embarrassing. I don't want to be a burden to my parents," said McCune, adding that he felt like a high school dropout.
Economists, analysing government data, estimate about 4 million fewer people are in the labour force than in December 2007, primarily due to a lack of jobs rather than the normal aging of America's population. The size of the shift underscores the severity of the jobs crisis.
If all those so-called discouraged jobseekers had remained in the labor force, August's jobless rate of 8.1 per cent would have been 10.5 per cent.
The jobs crisis spurred the Federal Reserve last week to launch a new bond-buying program and promise to keep it running until the labor market improves. It also poses a challenge to President Barack Obama's re-election bid.
The labour force participation rate, or the proportion of working-age Americans who have a job or are looking for one has fallen by an unprecedented 2.5 percentage points since December 2007, slumping to a 31-year low of 63.5 per cent.
"We never had a drop like that before in other recessions. The economy is worse off than people realize when people just look at the unemployment rate," said Keith Hall, senior research fellow at the Mercatus Center at George Mason University in Arlington, Virginia.
The participation rate would be expected to hold pretty much steady if the economy was growing at a normal pace. Only about a third of the drop in the participation rate is believed to be the result of the aging U.S. population.
The economy lost 8.7 million jobs in the 2007-09 recession and has so far recouped a little more than half of them.
Economists say jobs growth of around 125,000 per month is normally needed just to hold the jobless rate steady.
Given the likelihood that Americans will flood back into the labor market when the recovery gains traction, a pace twice that strong would be needed over a sustained period to make progress reducing the unemployment rate.
Last month, employers created just 96,000 jobs.
Roslyn Swan lost her job in 2007 as a portfolio associate at a financial firm in New York. After submitting hundreds of applications, the 44-year-old is taking a break.
"Maybe after the elections," Swan said of her next attempt to get work. "I know that I will be employed again. I don't know when, but I know it will happen."
Americans of all ages are leaving the workforce, but the problem is most acute in the 20-24 age group, where the participation rate has plunged by 4.4 percentage points since December 2007.
Many Americans typically start working in their teens, taking part-time jobs after school and over summer vacations, a tradition that is supposed to instill a work ethic. With many failing to secure jobs after graduating from high school and college, analysts worry about U.S. competitiveness.
"Because of delays to their career, the skills set accumulation that normally happens in the first or third job is not happening," said Paul Conway, president of Generation Opportunity in Washington, a non-profit, non-partisan organization that works with 18- to 29-year-olds on economic issues.
Last month, the proportion of 20- to 24-year-olds in the labor force was its lowest since 1972. Other age categories are faring little better. The 25-54 age group has seen a decline of 1.8 percentage points since December 2007.
Some, like 27-year-old Casey Potts, have gone back to school. She is studying nursing in Kentucky after losing her medical sales job.
"If I had stayed in medical sales, I would be job searching now," said Potts.
But separate surveys by the Economic Policy Institute (EPI) and Generation Opportunity found little evidence that young people were going back to school when unable to land a job.
One deterrent is the rising cost of education and record levels of student debt. About two-thirds of 2012 college graduates left school in debt, owing on average $28,700 in student loans, according to Mark Kantrowitz, publisher of FinAid.org.
"Young people dropping out of the labor force to go back to school would be a silver lining if it were true," said Heidi Shierholz, a senior EPI economist, adding that enrollment had gradually been increasing for decades.
A Generation Opportunity survey published in August showed a third of young people were putting off additional training and post-graduate studies because of the sour economy.
"This is significant. People are making the decision to put those off because the assurance of a return to investment is not there," said the non-profit's Conway, a veteran observer of the labor market as a former Department of Labor chief of staff.
He said his organization found that young people were doing unpaid internships at nonprofit groups and businesses to prevent their skills from atrophying. Others were joining the military.
Some economists say the participation rate does not paint a true picture because people find work in the informal sector, ranging from legal activities such as child care to crime in some cases.
"People are picking a buck here and there and not being reported in anybody's payroll," said Patrick O'Keefe, head of economic research at J.H. Cohn in Roseland, New Jersey.
"They will say they are not doing anything, even as they have a job and are being paid under the table," said O'Keefe, a former deputy assistant secretary at the Labor Department. "We do not know to what extent that is going on."