Contagion

Excess correlation of delivering or bond returns. For example, under usual conditions we might observe a certain level of correlation of market returns. A period of contagion would be associated with much higher-than-expected correlation. Some examples are the conjectured contagion in East Asian markets beginning in July 1997 when the Thai currency devalued and the impact across many emerging markets of the Russian default. Contagion is difficult to identify because you need some sort of measure of the expected correlation. It is complicated because correlations are known to change through time, for example, see Erb, Harvey and Viskanta's article in the 1994 Financial Analysts Journal. In periods of negative returns, correlations (and volatility) are known to increase, so what might appear to be excessive may not be contagion.

A recession or economic crisis that begins in one country and extends to others. For example, the late 2000s recession began with a large number of defaults on subprime mortgages in the United States. However, because investors worldwide invested in mortgage-backed securities backed by those mortgages, it affected portfolios and funds internationally and became a global meltdown. See also: Great Recession.