For more than half a century, men have been disappearing from the workforce.

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In the 1950s, nearly 98 percent of the workforce was made up of men. That number declined to 88.6 percent at the beginning of 2013. So, what gives?

"In recent years, industries that require braun rather than brains have taken a major hit and those were jobs mainly held by men," said Jim Hughes, Dean of the Edward J. Bloustein School of Planning at Public Policy at Rutgers. "That's old line manufacturing and construction. Those were hard hit during the recession and are just starting to come back now."

"So, part of it is due to the changing economy. Part of it is that the industries that are growing are knowledge-based. We now have a higher proportion of college graduates that are women. Increasing numbers of men don't want to receive a higher education which puts them at a severe disadvantage in the workforce."

"At the same time, in industries where jobs have been permanently eliminated, the former job holders have had a very hard time finding jobs that need their skills and the work they can find pays much less. In many cases, those workers get very discouraged and drop out of the labor force," said Hughes. "Increasing numbers are finding that the disability route is easier than it was in the past, so that provides them with an income floor for not participating in the workforce."

A growing number of men also have spent time in prison which makes it more difficult to find a job when they are released.