Barra Risk Model
Barra Risk Model
Handbook
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RV 03-2004
Contents
About Barra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
A Pioneer in Risk Management . . . . . . . . . . . . . . . . . . . . . . . . . . . v
Contacting Barra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .vi
Other Barra Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .vi
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
1. Forecasting Risk with Multiple-Factor Models . . . . . . . . . . . .1
What Are Multiple-Factor Models? . . . . . . . . . . . . . . . . . . . . . . . . 1
How Do Multiple-Factor Models Work? . . . . . . . . . . . . . . . . . . . . 2
Advantages of Multiple-Factor Models. . . . . . . . . . . . . . . . . . . . . . 2
An Illustration of Multiple-Factor Models . . . . . . . . . . . . . . . . . . . 3
Model Mathematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Single-Factor Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Multiple-Factor Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Multiple-Asset Portfolio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Risk Prediction with MFMs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
The Covariance Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Deriving the Variance-Covariance Matrix of Asset Returns. . . 10
Final Risk Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2. Forecasting Equity Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
A Historical Perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Barra’s Equity Multiple-Factor Model . . . . . . . . . . . . . . . . . . . . . 19
Common Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Risk Indices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Industries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Specific Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Contents
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3. Barra Equity Risk Modeling . . . . . . . . . . . . . . . . . . . . . . . . 21
Model Estimation Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Data Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Descriptor Selection and Testing . . . . . . . . . . . . . . . . . . . . . . . . . 24
Descriptor Standardization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Risk Index Formulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Industry Allocation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Factor Return Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Covariance Matrix Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Exponential Weighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Covariance Matrix Scaling: Computing Market Volatility . . . 29
Specific Risk Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Updating the Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4. Forecasting Fixed-Income Risk . . . . . . . . . . . . . . . . . . . . . . 39
A Historical Perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Barra’s Multiple-Factor Model . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Common Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Interest Rate Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Spread Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Specific Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.
Interest Rate Risk Modeling . . . . . . . . . . . . . . . . . . . . . . . . 51
Estimation Process Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Term Structure Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Interpolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Estimation Algorithm Implementation . . . . . . . . . . . . . . . . . 58
Factor Shape Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Factor Exposure Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Factor Return Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Term Structure Covariance Matrix Construction . . . . . . . . . . . . . 66
Covariance Matrix Rotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Updating the Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
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6. Spread Risk Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71
Swap Spread Risk Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Data Acquisition and Factor Return Estimation. . . . . . . . . . . 72
Factor Exposure Calculation . . . . . . . . . . . . . . . . . . . . . . . . . 72
Detailed Credit Spread Risk Model . . . . . . . . . . . . . . . . . . . . . . . 74
Currency Dependence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Model Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Data Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Factor Return Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Covariance Matrix Estimation. . . . . . . . . . . . . . . . . . . . . . . . 79
Factor Exposure Calculation . . . . . . . . . . . . . . . . . . . . . . . . . 80
Emerging-Market Risk Modeling . . . . . . . . . . . . . . . . . . . . . . . . 80
Model Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Data Acquisition and Factor Return Estimation. . . . . . . . . . . 82
Covariance Matrix Estimation. . . . . . . . . . . . . . . . . . . . . . . . 82
Factor Exposure Calculation . . . . . . . . . . . . . . . . . . . . . . . . . 83
Updating the Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
7. Specific Risk Modeling. . . . . . . . . . . . . . . . . . . . . . . . . . . . .85
Heuristic Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Data Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Sovereign, U.S. Agency, and MBS Specific Risk Estimation . . 86
Corporate Bond Specific Risk Estimation . . . . . . . . . . . . . . . 87
Transition-Matrix-Based Model. . . . . . . . . . . . . . . . . . . . . . . . . . 88
Data Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Transition Matrix Generation . . . . . . . . . . . . . . . . . . . . . . . . 89
Rating Spread Level Calculation . . . . . . . . . . . . . . . . . . . . . . 90
Credit Migration Forecasting . . . . . . . . . . . . . . . . . . . . . . . . 93
Updating the Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
8. Currency Risk Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . .99
Model Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Data Acquisition and Return Calculation . . . . . . . . . . . . . . . . . 100
Estimation of the Covariance Matrix . . . . . . . . . . . . . . . . . . . . . 100
Currency Correlation Model . . . . . . . . . . . . . . . . . . . . . . . . 101
Currency Volatility Model. . . . . . . . . . . . . . . . . . . . . . . . . . 102
Contents
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Volatility Across Markets . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Time-Scaling Currency Risk Forecasts . . . . . . . . . . . . . . . . . . . . 107
Updating the Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
9.
Integrated Risk Modeling . . . . . . . . . . . . . . . . . . . . . . . . . 111
Model Integration Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Building Global Asset Class Models . . . . . . . . . . . . . . . . . . . . . 112
The Structure of Local Models . . . . . . . . . . . . . . . . . . . . . . 113
Aggregating Local Models . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Implementing Global Factor Models . . . . . . . . . . . . . . . . . . 115
Consistency Between Local Models and Global Model . . . . 116
Global Equities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Global Equity Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
Exposures of Local Equity Factors to Global Equity Factors . 117
Estimating Returns to Global Equity Factors . . . . . . . . . . . . 117
Computing Covariances of Global Equity Factors . . . . . . . . 119
Scaling to Local Markets. . . . . . . . . . . . . . . . . . . . . . . . . . . 119
Global Bonds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Global Bond Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
Exposures of Local Bond Factors to Global Bond Factors. . . 124
Computing Covariances Of Global Bond Factors . . . . . . . . 124
The Currency Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
Putting It All Together—A Multi-Asset Class Risk Model . . . . . 127
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
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Handbook
About Barra
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About Barra
v
Contacting Barra
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Barra Risk Model
Handbook