Barra Risk Model
Barra Risk Model
Handbook
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RV 10-2007
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 Correlation . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Updating the Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
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6. Spread Risk Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69
Swap Spread Risk Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Data Acquisition and Factor Return Estimation. . . . . . . . . . . 70
Factor Exposure Calculation . . . . . . . . . . . . . . . . . . . . . . . . . 70
Detailed Credit Spread Risk Model . . . . . . . . . . . . . . . . . . . . . . . 71
Currency Dependence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Model Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Data Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Factor Return Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Covariance Matrix Estimation. . . . . . . . . . . . . . . . . . . . . . . . 77
Factor Exposure Calculation . . . . . . . . . . . . . . . . . . . . . . . . . 78
Emerging-Market Risk Modeling . . . . . . . . . . . . . . . . . . . . . . . . 78
Model Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Data Acquisition and Factor Return Estimation. . . . . . . . . . . 80
Covariance Matrix Estimation. . . . . . . . . . . . . . . . . . . . . . . . 80
Factor Exposure Calculation . . . . . . . . . . . . . . . . . . . . . . . . . 81
Updating the Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
7. Specific Risk Modeling. . . . . . . . . . . . . . . . . . . . . . . . . . . . .83
Heuristic Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Data Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Sovereign, U.S. Agency, and MBS Specific Risk Estimation . . 84
Corporate Bond Specific Risk Estimation . . . . . . . . . . . . . . . 85
Transition-Matrix-Based Model. . . . . . . . . . . . . . . . . . . . . . . . . . 86
Data Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Transition Matrix Generation . . . . . . . . . . . . . . . . . . . . . . . . 87
Rating Spread Level Calculation . . . . . . . . . . . . . . . . . . . . . . 88
Credit Migration Forecasting . . . . . . . . . . . . . . . . . . . . . . . . 91
Updating the Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
8. Currency Risk Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . .97
Model Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Data Acquisition and Return Calculation . . . . . . . . . . . . . . . . . . 98
Estimation of the Covariance Matrix . . . . . . . . . . . . . . . . . . . . . . 98
Currency Correlation Model . . . . . . . . . . . . . . . . . . . . . . . . . 99
Currency Volatility Model. . . . . . . . . . . . . . . . . . . . . . . . . . 100
Contents
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Volatility Across Markets . . . . . . . . . . . . . . . . . . . . . . . . . . 102
Time-Scaling Currency Risk Forecasts . . . . . . . . . . . . . . . . . . . . 105
Updating the Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
9.
Integrated Risk Modeling . . . . . . . . . . . . . . . . . . . . . . . . . 109
Model Integration Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Building Global Asset Class Models . . . . . . . . . . . . . . . . . . . . . 110
The Structure of Local Models . . . . . . . . . . . . . . . . . . . . . . 111
Aggregating Local Models . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Implementing Global Factor Models . . . . . . . . . . . . . . . . . . 113
Consistency Between Local Models and Global Model . . . . 114
Global Equities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
Global Equity Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Exposures of Local Equity Factors to Global Equity Factors . 115
Estimating Returns to Global Equity Factors . . . . . . . . . . . . 115
Computing Covariances of Global Equity Factors . . . . . . . . 117
Scaling to Local Markets. . . . . . . . . . . . . . . . . . . . . . . . . . . 117
Global Bonds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
Global Bond Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
Exposures of Local Bond Factors to Global Bond Factors. . . 122
Computing Covariances Of Global Bond Factors . . . . . . . . 122
The Currency Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
Putting It All Together—A Multi-Asset Class Risk Model . . . . . 125
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
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Barra Risk Model
Handbook
About Barra
In recent years the investment management industry has adjusted
to continuing changes—theoretical advances, technological devel-
opments, and volatility. To address these, investment managers
and financial institutions require the most advanced and powerful
analytical tools available.
A Pioneer in Risk Management
As the leading provider of global investment decision support
tools and innovative risk management technology, Barra has
responded to these industry changes by providing quantitative
products and services that are both flexible and efficient.
Barra products are a combination of advanced technology and
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models. In turn, these models are the basis of software products
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ysis, and historical performance attribution.
With more than 80 researchers in offices around the world and
products that cover most of the world’s traded securities, Barra
maintains one of the strongest risk management research practices
in the world today.
About Barra
v
Contacting Barra
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Other Barra Resources
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information on the topics discussed in this handbook.
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information, visit the Events Calendar at http://www.barra.com.
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Barra Risk Model
Handbook