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Chapter 9

Chapter 9. Capital Asset Pricing Model. It is the equilibrium model that underlies all modern financial theory Derived using principles of diversification with simplified assumptions Markowitz, Sharpe, Lintner and Mossin are researchers credited with its development.

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Chapter 9

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  1. Chapter 9 Capital Asset Pricing Model

  2. It is the equilibrium model that underlies all modern financial theory Derived using principles of diversification with simplified assumptions Markowitz, Sharpe, Lintner and Mossin are researchers credited with its development Capital Asset Pricing Model (CAPM)

  3. Individual investors are price takers Single-period investment horizon Investments are limited to traded financial assets No taxes and transaction costs Assumptions

  4. Information is costless and available to all investors Investors are rational mean-variance optimizers There are homogeneous expectations Assumptions Continued

  5. All investors will hold the same portfolio for risky assets – market portfolio Market portfolio contains all securities and the proportion of each security is its market value as a percentage of total market value Resulting Equilibrium Conditions

  6. Risk premium on the market depends on the average risk aversion of all market participants Risk premium on an individual security is a function of its covariance with the market Resulting Equilibrium Conditions Continued

  7. Figure 9.1 The Efficient Frontier and the Capital Market Line (CML)

  8. Capital Market Line (CML) E(rc) = rf +[(E(rM) – rf)/σM]σc CML describes return and risk for portfolios on efficient frontier

  9. The risk premium on individual securities is a function of the individual security’s contribution to the risk of the market portfolio An individual security’s risk premium is a function of the covariance of returns with the assets that make up the market portfolio Return and Risk For Individual Securities

  10. Economic Intuition Behind the CAPM Observation: Each investor holds the market portfolio and thus the risk of his/her portfolio is M2 M2 = i jWiWjij = i jWiWjCov(ri, rj) = iWi {jWjCov(ri, rj)} = iWi {W1Cov(ri, r1) + W2Cov(ri, r2) + …….. + WnCov(ri, rn)} = iWi {Cov(ri, W1r1) + Cov(ri, W2r2) + …….. + Cov(ri, Wnrn)} = iWi Cov(ri, W1r1 + W2r2 + …….. + Wnrn) = iWi Cov(ri, rM) Hence, M2 = W1 Cov(r1, rM) + W2 Cov(r2, rM) + …. + Wn Cov(rn, rM) Conclusion: Security i’s contribution to the risk of the market portfolio is measured by Cov(ri, rM).

  11. Note that M2 = W1 Cov(r1, rM) + W2 Cov(r2, rM) + …. + Wn Cov(rn, rM). Dividing both sides by M2, we obtain 1 = W1 Cov(r1, rM)/M2 + W2 Cov(r2, rM)/M2 + …. + Wn Cov(rn, rM)/M2. = W1 1 + W2 2 + .…. + Wn n. Conclusion: The risk of the market portfolio can be viewed as the weighted sum of individual stock betas. Hence, for those who hold the market portfolio, the proper measure of risk for individual stocks is beta.

  12. Implications: The risk premium for an individual security (portfolio) must be determined by its beta. Two stocks (portfolios) with the same beta should earn the same risk premium. {E(ri) - rf}/i={E(rj) - rf}/j ={E(rp) - rf}/p={E(rM) - rf}/M {E(ri) - rf}/i ={E(rM) - rf}/M {E(ri) - rf}/i ={E(rM) - rf}/1 E(ri) - rf ={E(rM) - rf}i E(ri) = rf +{E(rM) - rf}i : Security Market Line (SML)

  13. Figure 9.2 The Security Market Line

  14. Figure 9.3 The SML and a Positive-Alpha Stock

  15. The Index Model and Realized Returns To move from expected to realized returns—use the index model in excess return form: Rit = αi + βi RMt + eit where Rit = rit – rft and RMt = rMt – rft αi = Jensen’s alpha for stock i The index model beta coefficient turns out to be the same beta as that of the CAPM expected return-beta relationship

  16. Figure 9.4 Estimates of Individual Mutual Fund Alphas, 1972-1991

  17. The CAPM and Reality Is the condition of zero alphas for all stocks as implied by the CAPM met Not perfect but one of the best available Is the CAPM testable Proxies must be used for the market portfolio CAPM is still considered the best available description of security pricing and is widely accepted

  18. Econometrics and the Expected Return-Beta Relationship It is important to consider the econometric technique used for the model estimated Statistical bias is easily introduced Miller and Scholes paper demonstrated how econometric problems could lead one to reject the CAPM even if it were perfectly valid

  19. Extensions of the CAPM Zero-Beta Model Helps to explain positive alphas on low beta stocks and negative alphas on high beta stocks

  20. Black’s Zero Beta Model Absence of a risk-free asset Combinations of portfolios on the efficient frontier are efficient. All frontier portfolios have companion portfolios that are uncorrelated. Returns on individual assets can be expressed as linear combinations of efficient portfolios.

  21. Black’s Zero Beta Model Formulation

  22. Efficient Portfolios and Zero Companions E(r) Q P E[rz (Q)] Z(Q) Z(P) E[rz (P)] s

  23. Zero Beta Market Model CAPM with E(rz (m)) replacing rf

  24. Liquidity and the CAPM Liquidity Illiquidity Premium Research supports a premium for illiquidity. Amihud and Mendelson Acharya and Pedersen

  25. CAPM with a Liquidity Premium f (ci) = liquidity premium for security i f (ci) increases at a decreasing rate

  26. Figure 9.5 The Relationship Between Illiquidity and Average Returns

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