问题如下:
Your bank calculates a one-day 95% VAR for market risk, a one-year 99% VAR for operational risk, and a one-year 99% VAR for credit risk. The measures are $100 million, $500 million, and $1 billion, respectively. Operational risk is defined to include all risks that are not market risks and credit risks, and these three categories are mutually uncorrelated. The market risk VAR assumes normally distributed returns, and the bank expects to be successful to keep its market risk VAR at that level for the whole year. Your boss wants your best estimate of a firmwide VAR at the 1% level. Among the following choices, your best estimate is:
选项: $1.7 billion
$1.94 billion
C.$2.50 billion
D.It is impossible to aggregate risks with different distributions having only this information.
解释:
C is correct. First, we convert the daily VAR at the 95% level to the same parameters as the other. With the normality assumption, this is VARMKT = $100 x (2.326/ 1.645) = $2,245. We then combine the three VARs by taking the square root of the sum of squares, which gives VAR = = $2,458.
置信区间不相同的VaR之间有可比性吗?