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An Evaluation of Bank VaR Measures for Market Risk During and Before the Financial Crisis

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.