the difference being in numbers. According to the NBER, a recession is "a significant decline in activity spread across the economy, lasting more than a few months, visible in industrial production, employment, real income, and wholesale-retail trade." Contrary to popular wisdom, recession is not tied directly to a decline in the gross domestic product. The gross domestic product is measured only quarterly and is continually revised (often years later), and the NBER prefers to use monthly indicators such as employment, personal income, and manufacturing sales. Over the four years from 1929 to 1933, production at the nation's factories, mines, and utilities fell by more than half. People's real disposable incomes dropped 28 percent. Stock prices collapsed to one-tenth of their pre-crash height. The number of unemployed Americans rose from 1.6 million in 1929 to 12.8 million in 1933. One of every four workers was out of a job Recession = short term Depression = Long term in greater numbers