投资学：Chap027

1、INVESTMENTS | BODIE, KANE, MARCUS Copyright 2011 by The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill/Irwin CHAPTER 27 The Theory of Active Portfolio Management INVESTMENTS | BODIE, KANE, MARCUS 27-2 Overview Treynor-Black model The optimization uses analysts forecasts of superior per

2、formance. The model is adjusted for tracking error and for analyst forecast error. Black-Litterman model INVESTMENTS | BODIE, KANE, MARCUS 27-3 Table 27.1 Construction and Properties of the Optimal Risky Portfolio INVESTMENTS | BODIE, KANE, MARCUS 27-4 Spreadsheet 27.1 Active Portfolio Management IN

3、VESTMENTS | BODIE, KANE, MARCUS 27-5 Spreadsheet 27.1 An active portfolio of six stocks is added to the passive market index portfolio. Table D shows: Performance increases are very modest. M-square increases by only 19 basis points. INVESTMENTS | BODIE, KANE, MARCUS 27-6 Table 27.2 Stock Prices and

4、 Analysts Target Prices for June 1, 2006 Lets add these new forecasts to the spreadsheet model and re-calculate Table D. INVESTMENTS | BODIE, KANE, MARCUS 27-7 Figure 27.1 Rates of Return on the S&P 500 (GSPC) and the Six Stocks INVESTMENTS | BODIE, KANE, MARCUS 27-8 Table 27.3 The Optimal Risky Por

5、tfolio INVESTMENTS | BODIE, KANE, MARCUS 27-9 Results The Sharpe ratio increases to 2.32, a huge risk-adjusted return advantage. M-square increases to 25.53%. INVESTMENTS | BODIE, KANE, MARCUS 27-10 Results Problems: The optimal portfolio calls for extreme long/short positions that may not be feasib

6、le for a real-world portfolio manager. The portfolio is too risky and most of the risk is nonsystematic risk. A solution: Restrict extreme positions. This results in a lack of diversification. INVESTMENTS | BODIE, KANE, MARCUS 27-11 Table 27.4 The Optimal Risky Portfolio with Constraint on the Activ

7、e Portfolio (wA 1) INVESTMENTS | BODIE, KANE, MARCUS 27-12 Figure 27.2 Reduced Efficiency when Benchmark is Lowered Benchmark risk is the standard deviation of the tracking error, TE = RP-RM. Control it by restricting WA. INVESTMENTS | BODIE, KANE, MARCUS 27-13 Table 27.5 The Optimal Risky Portfolio

8、 with the Analysts New Forecasts INVESTMENTS | BODIE, KANE, MARCUS 27-14 Adjusting Forecasts for the Precision of Alpha How accurate is your forecast? Regress forecast alphas on actual, realized alphas to adjust alpha for the accuracy of the analysts previous forecasts. INVESTMENTS | BODIE, KANE, MA

9、RCUS 27-15 Figure 27.4 Organizational Chart for Portfolio Management INVESTMENTS | BODIE, KANE, MARCUS 27-16 The Black-Litterman Model The Black-Litterman model allows portfolio managers to incorporate complex forecasts (called “views”) into the portfolio construction process. Historical returns, ev

10、en over long periods, have very limited power to infer expected returns for the next month. The business cycle and other macroeconomic variables may be better forecasters of expected returns. Historical variance is a good predictor of expected future variance. INVESTMENTS | BODIE, KANE, MARCUS 27-17

11、 Steps in the Black-Litterman Model 1. Estimate the covariance matrix from recent historical data. 2. Determine a baseline forecast. 3. Integrate the managers private views. 4. Develop revised (posterior) expectations. 5. Apply portfolio optimization. INVESTMENTS | BODIE, KANE, MARCUS 27-18 Figure 2

12、7.5 Sensitivity of Black-Litterman Portfolio Performance to Confidence Level INVESTMENTS | BODIE, KANE, MARCUS 27-19 Figure 27.6 Sensitivity of Black-Litterman Portfolio Performance to Confidence Level INVESTMENTS | BODIE, KANE, MARCUS 27-20 BL Conclusions The Black-Litterman (BL) model and the Blac

13、k-Treynor (TB) model are complements. The models are identical with respect to the optimization process and will chose identical portfolios given identical inputs. The BL model is a generalization of the TB model that allows you to have views about relative performance that cannot be used in the TB

14、model. INVESTMENTS | BODIE, KANE, MARCUS 27-21 BL vs. TB Black-Litterman Model Optimal portfolio weights and performance are highly sensitive to the degree of confidence in the views. The validity of the BL model rests largely upon the way in which the confidence about views is developed. Treynor-Bl

15、ack Model TB model is not applied in the field because it results in “wild” portfolio weights. The extreme weights are a consequence of failing to adjust alpha values to reflect forecast precision. INVESTMENTS | BODIE, KANE, MARCUS 27-22 BL vs. TB Black-Litterman Model Use the BL model for asset all

16、ocation. Views about relative performance are useful even when the degree of confidence is inaccurately estimated. Treynor-Black Model Use the TB model for the management of security analysis with proper adjustment of alpha forecasts. INVESTMENTS | BODIE, KANE, MARCUS 27-23 Value of Active Managemen

17、t Kane, Marcus, and Trippi show that active management fees depend on: 1.the coefficient of risk aversion, 2.the distribution of the squared information ratio in the universe of securities, 3.the precision of the security analysts. INVESTMENTS | BODIE, KANE, MARCUS 27-24 Table 27.6 M-Square for the Portfolio, Actual Forecasts INVESTMENTS | BODIE, KANE, MARCUS 27-25 Table 27.7 M-Square of Simulated Portfolios INVESTMENTS | BODIE, KANE, MARCUS 27-26 Concluding Remarks The gap between t