CAViaR : Conditional Value at Risk By Regression Quantiles Robert Engle and Simone Manganelli U.C.S.D. July 1999 Value at Risk is a single measure of market risk of a firm, portfolio, trading desk, or other economic entity. It is defined by a significance level and a horizon. For convenience consider 5% and 1 day. Any loss tomorrow will be less than the Value at Risk with 95% certainty 2 HISTOGRAM OF TOMORROW’S VALUE - BASED ON PAST RETURNS K e r n e l D e n s ity ( N o r m a l, h = 0 .1 1 4 5 ) 0 .8 0 .6 0 .4 0 .2 0 .0 -20 -15 -10 S & P 500 -5 % 0 5 R E T U R N S 3 CUMULATIVE DISTRIBUTION Empirical CDF of S&P500 RETURNS 1.0 0.8 0.6 0.4 0.2 0.0 -20 -10 0 10 4 Weakness of this measure • The amount we exceed VaR is important • There is no utility function associated with this measure • The measure assumes assets can be sold at their market price - no consideration for liquidity • But it is simple to understand and very widely used. 5 THE PROBLEM • FORECAST QUANTILE OF FUTURE RETURNS • MUST ACCOMMODATE TIME VARYING DISTRIBUTIONS • MUST HAVE METHOD FOR EVALUATION • MUST HAVE METHOD FOR PICKING UNKNOWN PARAMETERS 6 TWO GENERAL APPROACHES • FACTOR MODELS--- AS IN RISKMETRICS • PORTFOLIO MODELS--- AS IN ROLLING HISTORICAL QUANTILES 7 FACTOR MODELS – Volatilities and correlations between factors are estimated – These volatilities and correlations are updated daily – Portfolio standard deviations are calculated from portfolio weights and covariance matrix – Value at Risk computed assuming normality 8 PORTFOLIO MODELS • Historical performance of fixed weight portfolio is calculated from data bank • Model for quantile is estimated • VaR is forecast 9 COMPLICATIONS • Some assets didn’t trade in the pastapproximate by deltas or betas • Some assets were traded at different times of the day - asynchronous pricessynchronize these • Derivatives may require special assumptions - volatility models and greeks. 10 PORTFOLIO MODELS - EXAMPLES • Rolling Historical : e.g. find the 5% point of the last 250 days • GARCH : e.g. build a GARCH model to forecast volatility and use standardized residuals to find 5% point • Hybrid model: use rolling historical but weight most recent data more heavily with exponentially declining weights. 11 THE CAViaR STRATEGY • Define a quantile model with some unknown parameters • Construct the quantile criterion function • Optimize this criterion over the historical period • Formulate diagnostic checks for model adequacy • Try it out! 12 Mathematical Formulation Find VaR satisfying P( y VaR ) t t 1 where y are returns and is probability Must be able to calculate VaR one day in advance and to estimate unknown parameters. 13 SPECIFICATIONS FOR VaR • VaR is a function of observables in t-1 • VaR=f(VaR(t-1), y(t-1), parameters) • For example - the Adaptive Model VaR VaR (hit ) t 1 t t 1 hit I ( y VaR ) t t t 14 How to compute VaR If beta is known, then VaR can be calculated for the adaptive model from a starting value. Let VaR(1) 1.65 * .95 if hit in 1 VaR(2) VaR(1) * (-.05) if no hit VaR (3) ..... 15 CAViaR News Impact Curve 16 More Specifications • Proportional Symmetric Adaptive VaRt VaRt 1 1( yt 1 VaRt 1 ) 2 ( yt 1 VaRt 1 ) • Symmetric Absolute Value: VaRt 1 0 1VaRt 1 2 yt 1 • Asymmetric Absolute Value: VaRt 1 0 1VaRt 1 2 yt 1 3 17 • Asymmetric Slope VaRt 0 1VaRt 1 2 yt 1 3 yt 1 • Indirect GARCH VaR 2 t 1 VaRt k 0 1 2 yt 1 k 2 1/ 2 18 19 Koenker and Bassett(1978) maximize Q( ) yt f t I y f t ( ) 0 1 2 hitt ( ) yt f t ( ) Where f is the quantile which depends on past information and parameters beta The criterion minimizes absolute errors where positive and negative errors are weighted differently 20 Quantile Objective Function 21 Even though the quantile function is nondifferentiable at some points, the first order conditions must be satisfied with probability one. hitt ( ˆ )ft / 0 X t ( ) f t / hit ' X 0 Hits should be unpredictable and are uncorrelated with regressors at an optimum 22 Adaptive Criterion -0.108 -0.110 -0.112 -0.114 -0.116 -0.118 500 1000 1500 2000 2500 3000 Quantile Criterion - Adaptive 23 Asymmetric Criterion -0.12 -0.13 -0.14 -0.15 -0.16 -0.17 500 1000 1500 2000 2500 3000 Likelihood from CAViaR1 24 Optimization by Genetic Algorithm • DIFFERENTIAL EVOLUTIONARY GENETIC ALGORITHM - Price and Storn(1997) • Start with initial population of trial values • Reproduction based on fitness • Crossover to find next generation • Mutation - random new elements • Stopping Criterion 25 Testing the Model • Should have the right proportion of hits • Should have no autocorrelation • Probability of exceeding VaR should be independent of VaR (no measurement error) • Should be testable both in-sample and outof-sample 26 27 Tests • Cowles and Jones (1937) • Runs - Mood (1940) • Ljung Box on hits (1979) • Dynamic Quantile Test 28 Dynamic Quantile Test To test that hits have the same distribution regardless of past observables Regress hit on – – – – – constant lagged hits Value at Risk lagged returns other variables such as year dummies 29 Distribution Theory • If out of sample test , or • If all parameters are known • Then TR02 will be asymptotically Chi Squared and F version is also available • But the distribution is slightly different otherwise 30 Mathematical Statistics References • Koenker and Bassett(1978) no dynamics • Weiss(1991) least absolute deviation • Newey and McFadden(1994) 31 Mathematical Statistics Q I yt f t yt f t n ˆ arg max Q( )n arg max subject to r( )0 Q( ) Then 1 1 1 1 1 1 LM n hit ' XD R' RD AD R' R D X ' hit d 1 1 ˆ n 0 N 0, (1 ) D AD 32 Mathematical Assumptions (1) E Q ( ) Q0 , is uniquely maximized at 0 p ( 2) r ( ) R (3) Q 1 hit t ( ) X t ( ), with probabilit y one n ( 4) 2 E Q D, non singular in a neighborho od of 0 1 p (5) h 0 X t X t ' D, where h is the density of (y-f) n ( 6) d n Q ( 0 ) N (0, A) p (7) X ' X / n A, a non - singular matrix (8) Q Q 0 Q 0 0 D 0 / 2 remainder , and remainder/ 1 n 0 0 p 33 Estimating Standard Errors • To calculate standard errors-must estimate D • D weights X by the height of the conditional density of returns at the estimated quantile • Should estimate this without making assumptions on the shape of the density 1 p ht 0 X t X t ' D, n where ht is the conditiona l density of yt -ft 34 A Picture Gives Intuition STANDARD DEVIATION OF Y1 IS TWICE Y2 BOTH ARE GAUSSIAN 1.0 0.8 0.6 0.4 0.2 0.0 200 400 600 Y1 800 1000 Y2 35 1% QUANTILE POINTS 1.0 0.8 0.6 0.4 0.2 0.0 200 400 Y1 Y2 600 800 1000 Q1_1/10 Q2_1/10 36 1% QUANTILE POINTS 0.25 0.20 0.15 0.10 0.05 0.00 220 240 260 280 300 Y1 Y2 320 340 360 380 400 Q1_1/10 Q2_1/10 37 5% QUANTILE 0.5 0.4 0.3 0.2 0.1 0.0 300 320 340 360 Y1 Y2 380 400 420 440 Q1_5/5 Q2_5/5 38 Density of Y2 divided by its standard deviation 0.5 0.4 0.3 0.2 0.1 0.0 200 400 Y1 Y2/2 600 800 1000 Q1_5/10 Q2_5/10 39 Assumption • Define t yt f t ~ gt ft gt ht ft • Therefore ht (0) gt (0) / ft • And • NOW ASSUME: gt (u ) g (u ) for all t for a Neighborhood of 0. 40 Estimate g Non-parametrically: 1 gˆ 0 cn n k t / cn • where k is a uniform kernel accepting points between -1 and 1 • and for 2900 observations empirically we chose cn=.05 hˆt (0) gˆ (0) / fˆt 41 42 A little Monte Carlo • 100 samples of 2000 observations of GARCH(1,1) with parameters (.3, .05, .90) • Estimate with Indirect GARCH CAViaR model • Mean parameters are (.42, .05, .88) • Some are far off showing no persistence • Trimming 10 extremes, means become (.31,.05,.90 ) 43 Table 1 - Summary statistics of the Monte Carlo experiment 0.1% True mean GAMMA1 GAMMA2 GAMMA3 4.15 0.90 0.69 7.16 0.80 0.67 t-statistic 8.54 -13.60 -0.95 Median 2.90 0.89 0.53 125.16 -2.45 2.60 -2.45 0.05 -0.07 2.60 -0.07 0.32 Mean Var-Cov matrix 1% True mean GAMMA1 GAMMA2 GAMMA3 1.62 0.90 0.27 2.28 0.87 0.30 t-statistic 7.59 -7.91 6.01 Median 1.57 0.90 0.27 7.79 -0.28 0.19 -0.28 0.01 -0.01 0.19 -0.01 0.02 Mean Var-Cov matrix 44 5% True mean Trimmed Mean Trimmed Median Trimmed Var-Cov matrix 25% True mean Trimmed Mean Trimmed Median Trimmed Var-Cov matrix GAMMA1 0.81 0.99 0.81 0.49 -0.04 0.02 GAMMA2 0.90 0.89 0.90 -0.04 0.00 0.00 GAMMA3 0.135 0.14 0.14 0.02 0.00 0.00 GAMMA1 0.13 0.18 0.13 0.03 -0.01 0.00 GAMMA2 0.90 0.88 0.90 -0.01 0.01 0.00 GAMMA3 0.027 0.03 0.02 0.00 0.00 0.00 45 Table 2 - Monte Carlo summary statistics after trimming the samples with GAMMA2<0.5 0.1% True mean Trimmed Mean Trimmed Median Trimmed Var-Cov matrix 1% True mean Trimmed Mean Trimmed Median Trimmed Var-Cov matrix GAMMA1 4.15 4.04 2.49 18.36 -0.40 0.81 GAMMA2 0.90 0.87 0.90 -0.40 0.01 -0.03 GAMMA3 0.69 0.60 0.50 0.81 -0.03 0.23 GAMMA1 1.62 2.02 1.55 2.72 -0.11 0.12 GAMMA2 0.90 0.88 0.90 -0.11 0.00 -0.01 GAMMA3 0.27 0.29 0.27 0.12 -0.01 0.02 46 Applications • Daily data from April 7, 1986 to April 7, 1999 3392 observations • Save the last 500 for out- of- sample tests • GM, IBM, S&P500 • Fit all 6 models for 5% ,1% , .1% and 25% VaR. 47 20 10 0 - 10 - 20 - 30 500 1000 1500 2000 2500 3000 GM 20 10 0 - 10 - 20 - 30 500 1000 1500 2000 2500 3000 IBM 10 0 - 10 - 20 - 30 500 1000 1500 2000 2500 3000 S&P500 48 News Impact Curve - 1% SP 12 10 8 6 4 2 200 400 VAR_ADAPTIVE VAR_ASY_ABS VAR_ASY_SLOP 600 800 1000 VAR_IND_GARCH VAR_PRO_SYM_ADA VAR_SYM_ABS 49 Caviar News Impact Curves SP500 at 5% 5 5 5 4 4 4 3 3 3 2 2 2 1 1 1 0 0 50 100 150 200 250 300 350 400 0 50 100 150 A 200 250 300 350 400 50 5 4 4 4 3 3 3 2 2 2 1 1 1 0 0 150 200 AAV 250 300 350 400 200 250 300 350 400 250 300 350 400 SAV 5 100 150 PSA 5 50 100 0 50 100 150 200 AS 250 300 350 400 50 100 150 200 G 50 1% and 5% News Impact Curves 5 4 3 2 1 200 400 VAR_AS_5 600 800 1000 VAR_ASY_SLOP 51 Table 3 - Parameter estimates Statistics for the Adaptive model ADAPTIVE *** 5% Gamma 1 Standard Errors P-values RQ in sample RQ out of sample Hits in sample (%) Hits out of sample (%) DQ in sample (p-values) 1) [c, hit(-1 to -5)] 2) [VaR] 3) [c, hit(-1), VaR] 4) [c, hit(-1 to -5), VaR] DQ out of sample (p-values) 1) [c, hit(-1 to -5)] 2) [VaR] 3) [c, hit(-1), VaR] 4) [c, hit(-1 to -5), VaR] GM 0.22 0.03 0.00 553.26 100.84 4.91 6.40 IBM S&P 500 0.44 0.23 0.05 0.02 0.00 0.00 527.45 312.65 120.20 72.41 5.01 5.08 5.20 5.00 0.31 0.52 0.12 0.06 0.47 0.34 0.01 0.01 0.46 0.48 0.10 0.07 0.40 0.26 0.40 0.45 0.98 0.90 0.21 0.56 0.01 0.80 0.55 0.01 ADAPTIVE *** 25% Gamma 1 Standard Errors P-values RQ in sample RQ out of sample Hits in sample (%) Hits out of sample (%) DQ in sample (p-values) 1) [c, hit(-1 to -5)] 2) [VaR] 3) [c, hit(-1), VaR] 4) [c, hit(-1 to -5), VaR] DQ out of sample (p-values) 1) [c, hit(-1 to -5)] 2) [VaR] 3) [c, hit(-1), VaR] 4) [c, hit(-1 to -5), VaR] GM 0.021 0.004 0.000 1507 291.62 24.86 27.00 IBM S&P 500 0.012 0.017 0.003 0.003 0.000 0.000 1368 752 312.44 184 25.31 25.07 24.80 27.40 0.94 0.73 0.58 0.81 0.25 0.80 0.64 0.23 0.59 0.68 0.30 0.32 0.57 0.43 0.23 0.64 0.67 0.97 0.28 0.30 0.45 0.29 0.39 0.41 52 ASYM SLOPE *** 0.1% Gamma 1 Standard Errors P-values Gamma 2 Standard Errors P-values Gamma 3 Standard Errors P-values Gamma 4 Standard Errors P-values RQ in sample RQ out of sample Hits in sample (%) Hits out of sample (%) DQ in sample (p-values) 1) [c, hit(-1 to -5)] 2) [VaR] 3) [c, hit(-1), VaR] 4) [c, hit(-1 to -5), VaR] DQ out of sample (p-values) 1) [c, hit(-1 to -5)] 2) [VaR] 3) [c, hit(-1), VaR] 4) [c, hit(-1 to -5), VaR] LM test for VaR(t-2) GM 2.7753 0.4342 0.6130 2.0416 25.01 4.15 0.10 0.00 IBM S&P 500 1.0863 0.4325 0.6587 0.6871 1.1402 1.8655 2.8743 2.2849 29.27 18.15 5.93 3.65 0.10 0.14 0.00 0.00 - - - - - - ASYM SLOPE *** 1% Gamma 1 Standard Errors P-values Gamma 2 Standard Errors P-values Gamma 3 Standard Errors P-values Gamma 4 Standard Errors P-values RQ in sample RQ out of sample Hits in sample (%) Hits out of sample (%) DQ in sample (p-values) 1) [c, hit(-1 to -5)] 2) [VaR] 3) [c, hit(-1), VaR] 4) [c, hit(-1 to -5), VaR] DQ out of sample (p-values) 1) [c, hit(-1 to -5)] 2) [VaR] 3) [c, hit(-1), VaR] 4) [c, hit(-1 to -5), VaR] LM test for VaR(t-2) GM 0.3928 0.2216 0.0381 0.7983 0.0676 0.0000 0.2725 0.1148 0.0088 0.4437 0.1589 0.0026 169.30 28.48 1.00 1.40 IBM S&P 500 0.0572 0.1473 0.0580 0.0833 0.1623 0.0385 0.9427 0.8699 0.0227 0.0484 0.0000 0.0000 0.0512 0.0001 0.0616 0.1168 0.2029 0.4997 0.2474 0.5045 0.1006 0.2403 0.0070 0.0179 179.54 105.84 40.54 22.69 0.97 0.97 1.60 1.60 0.60 0.98 0.96 0.71 0.81 0.89 0.96 0.88 0.56 0.96 0.94 0.68 0.96 0.46 0.67 0.97 0.92 0.05 0.21 0.53 0.07 0.92 0.05 0.13 0.45 0.07 0.96 53 ASYM SLOPE *** 5% Gamma 1 Standard Errors P-values Gamma 2 Standard Errors P-values Gamma 3 Standard Errors P-values Gamma 4 Standard Errors P-values RQ in sample RQ out of sample Hits in sample (%) Hits out of sample (%) DQ in sample (p-values) 1) [c, hit(-1 to -5)] 2) [VaR] 3) [c, hit(-1), VaR] 4) [c, hit(-1 to -5), VaR] DQ out of sample (p-values) 1) [c, hit(-1 to -5)] 2) [VaR] 3) [c, hit(-1), VaR] 4) [c, hit(-1 to -5), VaR] LM test for VaR(t-2) GM 0.0704 0.0425 0.0488 0.9353 0.0222 0.0000 0.0411 0.0285 0.0745 0.1182 0.0399 0.0015 548.63 99.20 4.98 5.20 IBM S&P 500 0.0951 0.0410 0.0444 0.0221 0.0161 0.0316 0.8916 0.9026 0.0272 0.0239 0.0000 0.0000 0.0597 0.0307 0.0335 0.0469 0.0372 0.2565 0.2110 0.2841 0.0558 0.0895 0.0001 0.0008 515.72 300.76 121.05 72.05 4.91 4.98 7.40 6.80 0.83 0.98 0.97 0.89 0.74 0.87 0.97 0.82 0.69 0.94 0.64 0.74 0.92 0.97 0.96 0.95 0.96 0.03 0.06 0.00 0.01 0.77 0.00 0.20 0.13 0.00 0.94 ASYM SLOPE *** 25% Gamma 1 Standard Errors P-values Gamma 2 Standard Errors P-values Gamma 3 Standard Errors P-values Gamma 4 Standard Errors P-values RQ in sample RQ out of sample Hits in sample (%) Hits out of sample (%) DQ in sample (p-values) 1) [c, hit(-1 to -5)] 2) [VaR] 3) [c, hit(-1), VaR] 4) [c, hit(-1 to -5), VaR] DQ out of sample (p-values) 1) [c, hit(-1 to -5)] 2) [VaR] 3) [c, hit(-1), VaR] 4) [c, hit(-1 to -5), VaR] LM test for VaR(t-2) GM 0.0404 0.0298 0.0877 0.9132 0.0393 0.0000 0.0415 0.0193 0.0157 0.0290 0.0170 0.0441 1500.88 289.41 25.00 25.60 IBM S&P 500 0.0125 0.0014 0.0104 0.0047 0.1151 0.3820 0.9605 0.9481 0.0169 0.0212 0.0000 0.0000 0.0108 0.0288 0.0098 0.0192 0.1349 0.0664 0.0297 0.0288 0.0127 0.0175 0.0097 0.0502 1360.53 746.90 311.51 183.48 25.14 24.93 23.40 25.80 0.69 0.97 0.97 0.79 0.83 0.85 0.90 0.90 0.49 0.93 0.99 0.60 0.88 0.88 0.67 0.94 0.99 0.64 0.45 0.79 0.70 0.89 0.29 0.77 0.67 0.32 0.60 54 Value at Risk for GM 12 12 10 10 8 8 6 6 4 4 2 2 0 0 500 1000 1500 2000 2500 3000 500 1000 A _V A R 1500 2000 2500 3000 2500 3000 2500 3000 A A V _V A R 12 12 10 10 8 8 6 6 4 4 2 2 0 0 500 1000 1500 2000 2500 3000 500 1000 A S _V A R 1500 2000 G _V A R 12 12 10 10 8 8 6 6 4 4 2 2 0 0 500 1000 1500 2000 P S A _V A R 2500 3000 500 1000 1500 2000 S A V _V A R 55 Value at Risk for SP 14 14 12 12 10 10 8 8 6 6 4 4 2 2 0 -2 0 500 1000 1500 2000 2500 3000 500 1000 A _V A R 1500 2000 2500 3000 2500 3000 2500 3000 A A V _V A R 14 14 12 12 10 10 8 8 6 6 4 4 2 2 0 0 500 1000 1500 2000 2500 3000 500 1000 A S _V A R 1500 2000 G _V A R 14 14 12 12 10 10 8 8 6 6 4 4 2 2 0 0 500 1000 1500 2000 P S A _V A R 2500 3000 500 1000 1500 2000 S A V _V A R 56 57 Dynamic Quantile Test -SP Dependent Variable: SAV_HIT Sample: 5 2892 Included observations: 2888 Variable Coefficient Std. Error t-Statistic Prob. C SAV_HIT(-1) SAV_HIT(-2) SAV_HIT(-3) SAV_HIT(-4) SAV_VAR 0.0051 0.0397 0.0244 0.0252 -0.0044 -0.0034 0.5977 0.0334 0.1920 0.1781 0.8127 0.6002 R-squared Adjusted R-squared S.E. of regression Sum squared resid Log likelihood Durbin-Watson stat 0.0029 0.0012 0.2190 138.2105 291.2040 1.9999 0.0096 0.0187 0.0187 0.0187 0.0187 0.0066 0.5277 2.1277 1.3051 1.3468 -0.2370 -0.5241 Mean dependent var S.D. dependent var Akaike info criterion Schwarz criterion F-statistic Prob(F-statistic) 0.0006 0.2191 -0.1975 -0.1851 1.7043 0.1301 58 In-sample Dynamic Quantile Test SAV_OUT PSA_OUT G_OUT AS_OUT AAV_OUT GM IBM SP500 A_OUT 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 59 In-sample 1% Dynamic Quantile Test SAV_OUT PSA_OUT G_OUT AS_OUT AAV_OUT GM IBM SP500 A_OUT 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 60 Out of Sample DQ Test SAV_OUT PSA_OUT G_OUT AS_OUT AAV_OUT GM IBM SP500 A_OUT 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 61 Out of Sample 1% DQ Test SAV_OUT PSA_OUT G_OUT AS_OUT AAV_OUT GM IBM SP500 A_OUT 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 62 TRADITIONAL GARCH(1,1) : IBM C 0.133384 0.016911 ARCH(1) 0.112194 0.005075 GARCH(1) 0.851960 0.009923 VaR=1.65*standard deviation 63 DQ TESTS FOR NORMAL GARCH 0.25 0.2 0.15 GM IBM SP500 0.1 0.05 0 IN-SAMPLE IN - TEST2 OUT OUT-TEST2 64 TRADITIONAL GARCH(1,1) : IBM C 0.133384 0.016911 ARCH(1) 0.112194 0.005075 GARCH(1) 0.851960 0.009923 5% POINT OF STANDARDIZED RESIDUALS = 1.48 FOR GM THIS POINT IS 1.56 FOR S&P THIS POINT IS 1.64 65 DQ TESTS FOR TRADITIONAL GARCH 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 GM IBM SP500 IN-SAMPLE IN - TEST2 OUT OUT-TEST2 66 Value at Risk for GM Asymmetric 20 10 0 -10 -20 -30 500 1000 1500 GM 2000 2500 3000 -AS_VAR 67 Value at Risk for IBM Adaptive 20 10 0 -10 -20 -30 500 1000 1500 IBM 2000 2500 3000 -A_VAR 68 Value at Risk for SP Implicit GARCH 10 0 -10 -20 -30 500 1000 1500 SP500 2000 2500 3000 -G_VAR 69 Some Extensions • Are there economic variables which can predict tail shapes? • Would option market variables have predictability for the tails? • Would variables such as credit spreads prove predictive? • Can we estimate the expected value of the tail? 70 CONCLUSIONS-Contributions? • Estimation strategy for VaR Models • New Dynamic Specifications of Quantiles • Estimation of VaR without estimating volatility • Test for VaR accuracy both in and out of sample • Promising empirical evidence on some specifications 71