Copula-Based Factor Model for Credit Risk Analysis

Transcription

1 Copula-Based Factor Model for Credit Risk Analysis Meng-Jou Lu Cathy Yi-Hsuan Chen Wolfgang Karl Härdle Ladislaus von Bortkiewicz Chair of Statistics HumboldtUniversität zu Berlin C.A.S.E. Center for Applied Statistics and Economics National Chiao Tung University Department of Finance Chung Hua University lvb.wiwi.hu-berlin.de case.hu-berlin.de nctu.edu.tw

2 Motivation 1-1 Systematic Risk Figure 1: Credit Risk depends the state of economy.

3 Motivation 1-2 Figure 2: Annual Default Counts from

4 Motivation 1-3 Figure 3: Annual average Loss Given Default rate: IG, SG and All, from

5 Motivation 1-4

6 Motivation 1-5 Objectives (i) Credit Risk Modeling Factor loading conditional on hectic and quiet state. State-dependent recovery rate. (ii) Model Comparison Four models

7 Motivation 1-6 Implication to Basel III Highlight systemic risk after crisis. Credit risk versus business cycle. How credit risk moves over the business cycle. Contribution of systematic risk on credit risk is state-dependent.

8 Motivation 1-7 Standard Technology Default event modeling Latent variable is a linear combination of systematic and idiosyncratic shocks. Copula enables exible and realistic default dependence structure.

9 Outline 1. Motivation 2. Factor Copulae & Stochastic Recoveries 3. Methodology 4. Empirical Results 5. Conclusions

10 Factor Copulae 2-1 Factor Copulae & Stochastic Recoveries Factor copula model is a exible measurement of portfolio credit risk: Krupskii and Joe (2013) Correlation breakdown structure: Ang and Bekaert (2002), Anderson et al. (2004) Recovery rate varies with the market conditions: Amraoui et al. (2012)

11 Factor Copulae 2-2 Candidate Models FC model - One-factor Gaussian copula model with constant correlation structure and constant recoveries. RFL model - Conditional factor loading and constant recoveries. RR model - One-factor Gaussian copula and stochastic recoveries. RRFL model - Conditional factor loading and stochastic recoveries.

12 Methodology 3-1 Default Modeling One-factor non-standardized Gaussian copula model U i = α i Z + 1 αi 2ε i i = 1,..., N. Z : systematic factor, ε i : idiosyncratic factors. Z and ε i are independent, and ε i are uncorrelated among each other, i=1,...,n. U i : the proxies for rm asset and liquidation value. Correlation coecient between U i and U j is ρ ij = α i α j σ 2. αi 2(σ2 1) + 1 αj 2(σ2 1) + 1

13 Methodology 3-2 The default indicator I {τ i t} = I [ Ui F 1 {P i (t)} ]. τ i indicates the default time of each obligor. F 1 ( ) donates the inverse cdf of any distribution. P i (t): hazard rate and marginal probability that obligor i defaults before t. From Moody's report. Extract from Credit spreads. Extract from Credit default swap spreads.

14 Methodology 3-3 Portfolio loss for each obligor L = N G i I {τ i t} = i=1 N [ G i I Ui F 1 {P i (t)} ]. i=1 G i is the loss given default (LGD) (i-th obligor's exposure = 1).

15 Methodology 3-4 Copulae For n dimensions distribution F with marginal distribution F X1,, F Xn, Copula function: F (x 1,, x n ) = C {F X1 (x 1 ),, F Xn (x n )} Hoeding on BBI:

16 Methodology 3-5 Conditional Default Model Conditional factor copulae model U i S=H = α H i Z + 1 (α H i ) 2 ε i U i S=Q = α Q i Z + 1 (α Q i ) 2 ε i α H, α Q link are conditional factor loading. Conditional default probability P(τ i < t S) = F F 1 {P i (t)} αi S Z = P i (Z S) 1 (αi S)2 S {H,Q} with P(S=H)=ω, and P(S=Q)=1 ω

17 Methodology 3-6 State-Dependent Recovery Rate The LGD on name i, G i (Z) is related to common factor Z and the marginal default probability P i link Given xed expected loss, (1 R i )P i = (1 R i ) P i [ F {F ( ] ) 1 P i α H i Z}/ 1 (α Hi ) 2 G i (Z S=H) = (1 R i ) [ ]. F {F 1 (P i ) αi H Z}/ 1 (α Hi ) 2 [ F {F ( ] ) 1 P i α Q G i (Z S=Q) = (1 R i Z}/ 1 (α Qi ) 2 i ) [ ]. F {F 1 (P i ) α Q i Z}/ 1 (α Qi ) 2 We set R i = 0 in the simplest case.

18 Methodology 3-7 Conditional Expected Loss Conditional default probability P i (Z S=H,Q) and conditional LGD, G i (Z S=H,Q), conditional expected loss, E(L i Z) = ωg i (Z S=H)P i (Z S=H)+(1 ω)g i (Z S=Q)P i (Z S=Q).

19 Methodology 3-8 Monte Carlo Simulation and MSE One-factor non-standardized Gaussian Copula Z N( 0.08, 1.02), ε i N(0, 1). Z and ε i are generated 1000 observations. Conditional probability that date t was belonging to the hectic is π(z = z). P(S = H Z = z) = π(z = z) = ωϕ(z θ H ) (1 ω)ϕ(z θ Q ) + ωϕ(z θ H ). αi H, α Q i are derived from the daily stock returns of S&P 500 and of collected default companies during the crisis period. Five-year period prior to the crisis period is the estimation period.

20 Methodology 3-9 Project to Default Time Using the denition of survival rate (Hull, 2006) τ i S = log{1 F (U i S)} P i. P i is the hazard rate and marginal probability that obligor i will default. τ i S is corresponding to E[I(τ i S < 1)] = P(τ i S < 1) = P i (Z S).

21 Methodology 3-10 State-Dependent Recovery Rate Simulation (1 R i )P i = (1 R i ) P i. P i is a adjusted default probability calibrated by plugging hazard rate P i link. R i is a lower bound for state-dependent recovery rates [0,1]. We set R i = 0 in the simplest case. Given α S i and simulated Z, we generate G i (Z S).

22 Methodology 3-11 Expected Loss Function With these two specications, we study the expected loss function under the given scenarios E(L i Z) = π(z = z)g i (Z S=H)P i (Z S=H) + (1 π(z = z))g i (Z S=Q)P i (Z S=Q) π(z = z) is better than unconditional probability ω.

23 Methodology 3-12 Estimation of the MSE Estimated Square Error (SE) SE = (actual default loss expected portfolio loss) 2. Actual default loss is from Moody's report. Calculate the mean of square errors referred to as Mean Square Error (MSE). Compare minimum MSE to evaluate FC, RFL, RR, and RRFL model.

24 Empirical Results 4-1 Data Forecast Period: 2008 and 2009 Daily USD S&P 500 and stock return of the defaults Estimated period: 5 years before the default year Source: Datastream

25 Empirical Results 4-2 Data Recovery rate: Realized recovery rate R i (weighted by volume) before default year by Moody's Hazard rate: Average historical default probability from Moody's report

26 Empirical Results 4-3 Empirical Results Model Probability Mean SD Period Unconditional (one normal) Conditional on quiet Conditional on hectic Period Unconditional (one normal) Conditional on quiet Conditional on hectic Table 1: Estimate Mixture of Normal Distribution by employing an EM algorithm SD means standard deviation

27 Empirical Results 4-4 Conditional Factor Loading Company Uncond. Quiet Hectic Abitibi-Consolidated Com. of Can Abitibi-Consolidated Inc FRANKLIN BANK GLITNIR BANKI LEHMAN BROS Table 2: Correlation coecients between S&P500 index returns and the return of default companies in 2008.

28 Empirical Results 4-5 (a) 2008 Lehman Bro. (b) 2009 E*TRADE Figure 4: The relationship between state-dependent recovery rates and S&P 500, Z. `*' in blue illustrates the pattern of state-dependent recovery rate, and `+' in red plots the recoveries proposed by Amraoui et al.(2012).

29 Empirical Results 4-6 Figure 5: The relationship between recovery rate and default probabilities, left panel 2008 and right panel 2009

30 Empirical Results 4-7 Estimation of MSE Company FC RFC RR RRFL Abitibi-Con. Com. of Can Abitibi-Con. Inc Franklin Bank Corp Glitnir banki hf Lehman Bro. Hold., Inc Table 3: The Estimated MSE of four dierent models for each default company in 2008.

31 Empirical Results 4-8 Empirical Results Year FC RFL RR RRFL Total % 3.2% 32.3% 61.3% % 7.9% 37.1% 50.0% Table 4: Number and Percentage of defaults with minimum MSE

32 Empirical Results 4-9 Basel III: Relative Contribution (a) 2008 (b) 2008 Figure 6: The 2D and 3D scatters plot of relative contribution The rst group (marked as `+' in green) indicates that they are generated in distress. The second group (marked as `*' in blue) indicates that they are generated in a bullish atmosphere. The third group (marked as `x' in red) collects the rest.

33 Conclusions 5-1 Conclusions (i) Model the dependence in a more exible and realistic way. Build the quiet and hectic regimes. Connect the recovery rate to the common factor. (ii) The conditional factor copulae together with state-dependent recoveries model could predict the default event during the crisis period. (iii) Coherent with the goals of Basel III.

34 Conclusions 5-2 Further Work (i) Alternative marginals: Generalized extreme value distribution or t-distribution. (ii) Alternative copula: t-copula.

35 Copula-Based Factor Model for Credit Risk Analysis Meng-Jou Lu Cathy Yi-Hsuan Chen Wolfgang Karl Härdle Ladislaus von Bortkiewicz Chair of Statistics HumboldtUniversität zu Berlin C.A.S.E. Center for Applied Statistics and Economics National Chiao Tung University Department of Finance Chung Hua University lvb.wiwi.hu-berlin.de case.hu-berlin.de nctu.edu.tw

36 Conclusions 5-4 References Amraoui, S. and Cousot, L. and Hitier, S. and Laurent, J. Pricing CDOs with state-dependent stochastic recovery rate Quantitative Finance 12(8): , 2012 Andersen, L. and J. Sidenius Extensions to the Gaussian: Random recovery and random factor loadings Journal of Credit Risk 1(1): 29-70, 2004

37 Conclusions 5-5 References Ang, A. and Bekaert, G. International asset allocation with regime shifts Review of Financial Studies 15(4): , 2002 Krupskii, P. and Harry, J. Factor copula model for multivariate data Journal of Multivariate Analysis 120: , 2013

38 Appendix 6-1 Conditional Factor Loading back (Z, U i ) ( [ µ Q N Z µ Q i N ( [ µ H Z µ H i ], ], [ (σ Q Z )2 (σ Q Z )αq (σ Q i ) [ (σ Q Z )αq (σ Q i ) (σz H)2 (σ Q i ) 2 (σz H)αH (σi H ) (σz H)αH (σi H ) (σi H ) 2 ] ) ] ) where P(S=H)=ω, P(S=Q)=1 ω Volatility in hectic periods is higher than in a quiet periods, σ H i > σ Q i. α Q and α H are the correlation coecient between each obligor and S&P 500 in quiet and hectic period