Survivorship bias

In finance, survivorship bias, also known as "survivor bias", refers to the tendency for mutual funds or hedge funds that have produced poor performance or low asset accumulations to be either liquidated or merged out of existence. In the case of long term global asset returns, survivorship bias comes into play with the extinction of whole markets due to war and or revolution. The result is an overestimation of past returns, as these poor returning funds/countries are dropped from the data base.