What happened to construction workers

Today builders say they are facing a profound shortage of qualified, trained workers.  Yet construction employment dropped by 2.3m jobs between 2006 and 2011 and is still 1.3m below the 2006 peak.  So what happened to over one million workers?  Why aren't they coming back in the market?

WSJ's Real Time Economics blog has the answer: some have switched to other industries but many have dropped out of the labor force.  At the same time hiring of young workers has been slow, so now there are not enough trained workers to meet demand.

This evidence further supports the view that despite the lowest employment to population ratio we have seen in 40 years, the labor market is close to having a balance between supply and demand.  Those who have dropped out of the labor market after they lost their jobs in the Great Recession do not appear to be coming back.