A recession is a decline in economic growth that is spread across the economy. A recession requires at least two consecutive quarters of negative economic growth. It is typically accompanied by falling gross domestic product, real income, industrial activity and wholesale-retail sales, and by rising unemployment. Historically, periods of recession were nearly as lengthy as periods of economic expansion. But since World War II, periods of expansion have lasted approximately five times as long as periods of recession. Most recently, the National Bureau of Economic Research found in December 2008 that a recession had begun in the U.S. during the previous December.