The charts reflect declining economic activity

A recession is commonly viewed by many students of economics as two consecutive quarterly declines in Gross Domestic Product (GDP) - the broadest measure of activity in the economy.

The National Bureau of Economic Research (NBER) does not define a recession in terms of two consecutive quarters of decline in real GDP.

Rather, a recession is a significant decline in economic activity spread across the economy, lasting more than a few months, normally visible in real GDP, real income, employment, industrial production, and wholesale-retail sales.

Since 1945, the economy has entered 12 recessions with an average length of 10 months.  The shortest contraction lasted six months and occurred in 1980.

The 1973-75 and 1981-82 recessions stretched out 16 months, making them the longest since WWII; however, the current cycle began in December 2007 and is likely surpass those recessions in length.

Just as it can take up to a year for the NBER to pinpoint the start of a recession, it can take just as long for the agency to declare that a business slump has ended. Therefore, 2010 may be well under way before we can officially state the Great Recession has been the longest in the post-war period.

For those keeping track, the longest slump started back in 1873 and lasted 65 months, which was followed by the 43-month contraction that began in 1929.  However, these declines in economic activity were classified as depressions as GDP declined by more than 10%.

Data Source: NBER

The series, Economy 101: What is ...? is also available.