"Well, it used to be if you looked demographically at who worked long hours it was low income people," Walden says. "They worked long hours simply because they had to to make more money.

"Now what we find is long hours are more likely to be worked by higher income people –- the folks that you would expect wouldn’t be working long hours because they are making a lot of money.

"And the reason for this appears to be that in today’s very competitive society, working long hours is one way to demonstrates to your boss or to the company that you are valuable, that you are productive," he adds. "It’s a signal that you are hard working and you hope by working these long hours that you eventually will be promoted and earn even more money later."

"So it’s really one of these things where people are doing it not so much to earn more money now but in hopes of getting much more money later."