Sunday, August 7, 2011

Market Risk Assessment -1

Quantification of risk is a major concern of financial players because it allows them to answer questions like "How can we lose with our portfolio in normal market conditions or abnormal for a time horizon given? ". VaR (Value at Risk) and Stress Testing are the two most common methods of quantification of risk and are usually combined.

Although the VaR can be used as a baseline measurement for all types of risk and the overall level of society, its most common use for market risk.
VaR is a probabilistic measure of the loss of a portfolio point of a given composition as a result of future changes in risk factors. It is defined by the maximum probable loss at a confidence level of x% (for a time horizon of one day / one week, etc.).. Var corresponds to the loss that will not be exceeded in more than (100-x)% of cases, when a position given structure is maintained for a period [0, T].

If Vt is the value of the position t, the VaR is given by:
Pr {Vo - VT} ≤ ≥ VaR (100 - x) / 100

For example, consider a portfolio for which the VaR of € 100 million with a confidence level of 99% over a period of one week, meaning that, under normal market conditions, there is a probability of 1 % to record a loss of more than € 100 million for the week of detention (period over which the change in value of the portfolio is measured).