Past downturns have been mere blips compared with the losses Americans faced last year, which set them back to below 2004 levels. “In the postwar period, we’ve never had anything other than very modest declines. That life experience led many people to think that houses were a one-way bet,” says Douglas Cliggott, the chief investment officer of Dover Management LLC…

In all, the net worth of U.S. households stood at $51.48 trillion at the end of 2008, the Fed data showed. Besides being down 17.9% from a year earlier, it was down 9% just from the third quarter.

The net-worth figure encompasses all of families’ assets — housing, stocks, personal property — minus their total debts.

Americans’ assets have taken further hits in the first two months of 2009, a period not covered in the quarterly report.