Traders work on the floor of the New York Stock Exchange, Monday, December 1, 2008. [Photo: China Daily/Agencies]

Related: Wall Street Plunges amid Economic Woes

               U.S. Manufacturing Sector Contracts for Fourth Straight Month

U.S. economy has been in a recession since December 2007, the National Bureau of Economic Research (NBER) said Monday.

The Business Cycle Dating committee of the NBER, a private, nonprofit research organization, said its members met by conference call on Friday.

And the committee "identified December 2007 as the peak month, after determining that the subsequent decline in economic activity was large enough to qualify as a recession."

"The peak marks the end of the expansion that began in November 2001 and the beginning of a recession. The expansion lasted 73 months; the previous expansion of the 1990s lasted 120 months," NBER said in a statement.

"A recession is a significant decline in economic activity spread across the economy, lasting more than a few months, normally visible in production, employment, real income and other indicators," the statement noted.

"A recession begins when the economy reaches a peak of activity and ends when the economy reaches its trough. Between trough and peak, the economy is in an expansion," it added.

The U.S. economy contracted by 0.2 percent and 0.5 percent at an annual rate in the fourth quarter of 2007 and the third quarter of 2008 respectively.

The classic definition of a recession is two consecutive quarters of negative GDP. Many economists believe the economy will continue to shrink in the fourth quarter and early next year.

The NBER said that they "do not identify economic activity solely with real GDP, but use a range of indicators" in determining the onset of recession.

Founded in 1920, the NBER has more than 1,000 university professors and researchers who act as bureau associates, studying how the economy works.

Meanwhile, the White House vowed it will take actions to save the economy. "What's important is what is being done about it," White House Spokesman Tony Fratto said on Monday, without using the word "recession."

"The most important things we can do for the economy right now are to return the financial and credit markets to normal, and to continue to make progress in housing, and that's where we'll continue to focus," he said.