The NBER defines a recession as "a significant decline in economic activity spread across the economy, lasting more than two quarters which is 6 months, normally visible in real gross domestic product (GDP), real income, employment, industrial production, and wholesale-retail sales".
In the 19th century, recessions frequently coincided with financial crises.
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The bank had some functions of a modern central bank, although it was responsible for only 20% of the young country's currency.
These periods of recession were not identified until the 1920s.
Their work is aided by historical patterns, in that recessions often follow external shocks to the economic system such as wars and variations in the weather affecting agriculture, as well as banking crises.
Major modern economic statistics, such as unemployment and GDP, were not compiled on a regular and standardized basis until after World War II.
In fact, many economists don't agree on the dates set by the NBER.
Federal Reserve Chairman Alan Greenspan -- a man who should know when a recession is in progress -- had predicted a recession about to begin in September 2008, when Lehman Brothers declared bankruptcy.
The average duration of the 11 recessions between 19 is 10 months, compared to 18 months for recessions between 19, and 22 months for recessions from 1854 to 1919.