James O'Brien and Pawel J. Szerszen
Abstract: We study the performance and behavior of Value at Risk (VaR) measures used by a number of large banks during and before the financial crisis. Alternative benchmark VaR measures, including GARCH-based measures, are also estimated directly from the banks' trading revenues and help to explain the bank VaR performance results. While highly conservative in the pre-crisis period, bank VaR exceedances were excessive and clustered in the crisis period. All benchmark VaRs were more accurate in the pre-crisis period with GARCH VaR measures the most accurate in the crisis period having lower exceedance rates with no exceedance clustering. Variance decompositions indicate a limited ability of the banks' VaR methodologies to adjust to the crisis-period market conditions. Despite their weaker performance, the bank VaRs exhibited greater predictive power for a measure of realized PnL volatility than benchmark VaR measures. Benchmark Expected Shortfall measures are also considered.
Keywords: Market risk, value at risk, backtesting, profit and loss, financial crisisFull paper (2 MB PDF)