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"Frontmatter". In: Analysis of Financial Time Series

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282 VALUEATRISKnext trading day. If the probability is 5%, which means that with probability 0.95 theloss will be less than or equal to the VaR for the next trading day, then the resultsobtained are1. $302,500 for the RiskMetrics,2. $287,200 for a Gaussian AR(2)-GARCH(1, 1) model,3. $283,520 for an AR(2)-GARCH(1, 1) model with a standardized Student-tdistribution with 5 degrees <strong>of</strong> freedom,4. $216,030 for using the empirical quantile, and5. $184,127 for applying the traditional extreme value theory using monthly minima(i.e., subperiod length n = 21).If the probability is 1%, then the VaR is1. $426,500 for the RiskMetrics,2. $409,738 for a Gaussian AR(2)-GARCH(1, 1) model,3. $475,943 for an AR(2)-GARCH(1, 1) model with a standardized Student-tdistribution with 5 degrees <strong>of</strong> freedom,4. $365,709 for using the empirical quantile, and5. $340,013 for applying the traditional extreme value theory using monthly minima(i.e., subperiod length n = 21).If the probability is 0.1%, then the VaR becomes1. $566,443 for the RiskMetrics,2. $546,641 for a Gaussian AR(2)-GARCH(1, 1) model,3. $836,341 for an AR(2)-GARCH(1, 1) model with a standardized Student-tdistribution with 5 degrees <strong>of</strong> freedom,4. $780,712 for using the empirical quantile, and5. $666,590 for applying the traditional extreme value theory using monthly minima(i.e., subperiod length n = 21).There are substantial differences among different approaches. This is not surprisingbecause there exists substantial uncertainty in estimating tail behavior <strong>of</strong> a statisticaldistribution. Since there is no true VaR available to compare the accuracy <strong>of</strong> differentapproaches, we recommend that one applies several methods to gain insight into therange <strong>of</strong> VaR.The choice <strong>of</strong> tail probability also plays an important role in VaR calculation. Forthe daily IBM stock returns, the sample size is 9190 so that the empirical quantiles<strong>of</strong> 5% and 1% are decent estimates <strong>of</strong> the quantiles <strong>of</strong> the return distribution. <strong>In</strong> thiscase, we can treat the results based on empirical quantiles as conservative estimates<strong>of</strong> the true VaR (i.e., lower bounds). <strong>In</strong> this view, the approach based on the traditionalextreme value theory seems to underestimate the VaR for the daily log returns <strong>of</strong> IBM

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