An extended period of depressed economic activity, typically a number of years, and potentially consisting of at least one and maybe two or more recessions, during which one or more of GDP, output, income, or employment, especially the latter, fail to rise above their level at the beginning of the period, even if GDP or output do recover fully much earlier in the period. The Great Depression of the 1930's contained two distinct recessions with significant recoveries of GDP and output after each, but with an ongoing very high level of unemployment and loss of income. The National Bureau of Economic Research's Business Cycle Dating Committee dates U.S. business cycles. There is no definition of depression on their website. It is popularly believed that a decrease of real GDP of 10% or greater would indicate a depression.