0. Return and Risk: The Capital Asset Pricing Model (CAPM)
Chapter 11
Return and Risk: The Capital Asset Pricing Model (CAPM)

1. Key Concepts and Skills
Know how to calculate expected returns
Know how to calculate covariances, correlations, and betas
Understand the impact of diversification
Understand the systematic risk principle
Understand the security market line
Understand the risk-return tradeoff
Be able to use the Capital Asset Pricing Model

2. Chapter Outline 11.1 Individual Securities
11.2 Expected Return, Variance, and Covariance
11.3 The Return and Risk for Portfolios
11.4 The Efficient Set
11.5 Riskless Borrowing and Lending
11.6 Announcements, Surprises, and Expected Return
11.7 Risk: Systematic and Unsystematic
11.8 Diversification and Portfolio Risk
11.9 Market Equilibrium
11.10 Relationship between Risk and Expected Return (CAPM)

3. 11.1 Individual Securities
The characteristics of individual securities that are of interest are the:
Expected Return
Variance and Standard Deviation
Covariance and Correlation (to another security or index)

4. 11.2 Expected Return, Variance, and Covariance
Consider the following two risky asset world:

5. Expected Return

6. Covariance
Deviation (離差) compares return in each state to the expected return.
Weighted takes the product of the deviations multiplied by the probability of that state.

7. Correlation (相關係數)

8. 11.3 The Return and Risk for Portfolios
Note that stock A has a higher expected return than Stock B and higher risk. Let us turn now to the risk-return tradeoff of a portfolio that is 60% invested in A and 40% invested in B.

9. Portfolios
Observe the decrease in risk that diversification offers: 0.6* *10.5%=18.7%>14.95%

10. 11.4 The Efficient Set

11. 11.4 The Efficient Set
將前頁各種權重之投資組合的期望報酬率與標準差描繪於縱軸為期望報酬率，橫軸為標準差的座標平面上，即可得到課本p.364的圖11.3。
該圖中有幾個重點: (p.364~365)
多角化發生於相關係數小於1
投資機會集代表投資人可以選擇的投資組合
效率集代表投資機會集當中的效率投組:

12. Portfolios with Various Correlations
Relationship depends on correlation coefficient (-1.0 <
< +1.0)
If = +1.0, no risk reduction is possible
If = –1.0, complete risk reduction is possible
return
100% A
 = -1.0
 = 1.0
 = 0.2
100% B 

13. The Efficient Set for Many Securities
return
Individual Assets P
Consider a world with many risky assets; we can still identify the opportunity set of risk-return combinations of various portfolios.

14. The Efficient Set for Many Securities
efficient frontier
return
minimum variance portfolio
Individual Assets P
The section of the opportunity set above the minimum variance portfolio is the efficient frontier.

15. 11.5 Riskless Borrowing and Lending
CML
return
Balanced fund rf 
Now investors can allocate their money across the T-bills (無風險資產)and a balanced mutual fund.

16. Riskless Borrowing and Lending
CML
return
efficient frontier rf P
With a risk-free asset available and the efficient frontier identified, we choose the capital allocation line with the steepest slope.

17. Riskless Borrowing and Lending
Example 11.3 (p.369): 考慮以下兩個資產的投資機會集
Common stock
Risk-free asset
Expected return
14%
10%
Standard deviation
20%

18. 11.7 Risk: Systematic
Risk factors that affect a large number of assets (系統性風險)
Also known as non-diversifiable risk or market risk
Includes such things as changes in GDP, inflation, interest rates, etc.

19. Risk: Unsystematic
Risk factors that affect a limited number of assets (非系統性風險)
Also known as unique risk and asset-specific risk
Includes such things as labor strikes, part shortages, etc.

20. 11.8 Diversification and Portfolio Risk
Diversification can substantially reduce the variability of returns without an equivalent reduction in expected returns.
This reduction in risk arises because worse than expected returns from one asset are offset by better than expected returns from another.
However, there is a minimum level of risk that cannot be diversified away, and that is the systematic portion (有些風險無法消除, 也就是系統風險).

21. Portfolio Risk and Number of Stocks
In a large portfolio the variance terms are effectively diversified away, but the covariance terms are not. 
Diversifiable Risk; Nonsystematic Risk; Firm Specific Risk; Unique Risk
Portfolio risk
Nondiversifiable risk; Systematic Risk; Market Risk n

22. Diversifiable Risk
The risk that can be eliminated by combining assets into a portfolio.
Often considered the same as unsystematic, unique, or asset-specific risk.
If we hold only one asset, or assets in the same industry, then we are exposing ourselves to risk that we could diversify away.

23. Total Risk(總風險) Total risk = systematic risk + unsystematic risk
The standard deviation of returns is a measure of total risk.
For well-diversified portfolios, unsystematic risk is very small.
Consequently, the total risk for a diversified portfolio is essentially equivalent to the systematic risk.

24. 11.9 Market Equilibrium
return
CML
efficient frontier M rf P
With the capital allocation line identified, all investors choose a point along the line—some combination of the risk-free asset and the market portfolio M. In a world with homogeneous expectations, M is the same for all investors.

25. Market Equilibrium
CML
return
Balanced fund rf 
Just where the investor chooses along the Capital Market Line depends on his risk tolerance.

26. Risk When Holding the Market Portfolio
Researchers have shown that the best measure of the risk of a security in a large portfolio is the beta of the security.
Beta measures the responsiveness of a security to movements in the market portfolio (i.e., systematic risk).

27. Estimating with Regression
Characteristic Line
Security Returns
Slope =
Return on market %
Ri = a i Rm + ei

28. 11.10 Risk and Return (CAPM) Expected Return on the Market:
Expected return on individual security
Market Risk Premium
This applies to individual securities held within well-diversified portfolios.

29. Expected Return on a Security
This formula is called the Capital Asset Pricing Model (CAPM):
Expected return on a security =
Risk-free rate +
Beta of the security ×
Market risk premium
Assume = 0, then the expected return is RF .
Assume = 1, then

30. Relationship Between Risk & Return
Expected return
1.0

31. Relationship Between Risk & Return
Expected return b
1.5

32. Quick Quiz
How do you compute the expected return and standard deviation for an individual asset? For a portfolio?
What is the difference between systematic and unsystematic risk?
What type of risk is relevant for determining the expected return?
Consider an asset with a beta of 1.2, a risk-free rate of 5%, and a market return of 13%.What is the expected return on the asset?
Expected return = (8) = 14.6%