The National Bureau of Economic Research has made official what we knew we knew, already: the recession is over. It ended -- that is, economic activity stopped declining -- in the early summer of 2009. The Great Recession lasted 18 months, two months longer than the 1981-2 recession to which it is often compared, and longer than any recession since World War II.

Gross Domestic Product has been growing for more than a year, so what took so long? NBER waits until it has enough information to identify exact peak and trough months. It waited until November 2008 to declare that there was a recession that began in December 2007, and it wanted 15 months to determine that the economy bottomed out in June 2009.

So, something obvious has been made official. Naturally, the stock market is going crazy.