Chapter 9 - Asset Pricing Models

Characteristics of the Market Portfolio

- All risky assets must be in portfolio, so it is completely diversified; includes only systematic risk - All securities included in proportion to their market value - Unobservable but proxied by S&P 500 - Contains worldwide assets; financial and real assets

Security Market Line (CAPM)

- CML Equation only applies to markets in equilibrium and efficient portfolios - The Security Market Line depicts the tradeoff between risk and expected return for individual securities - Under CAPM, all investors hold the market portfolio; how does an individual security contribute to the risk of the market portfolio? - A security's contribution to the risk of the market portfolio is based on beta

Risk Free Assets

- Certain-to-be-earned expected return and a variance of return of zero - No correlation with risky assets - Usually proxied by a Treasury security; amount to be received at maturity is free of default risk, known with certainty - Adding a risk-free asset extends and changes the efficient frontier

Estimating Beta:

- Treasury Bill rate used to estimate RF - Expected market return unobservable - Estimated using past market returns and taking an expected value Need: - Risk free rate data - Market portfolio data; S&P 500, DJIA, NASDAQ, etc. - Stock return data: Interval; Daily, monthly, annual, etc. - Length; One year, five years, ten years, etc. Use linear regression R=a+b(Rm-Rf)

Problems using Beta

- Which market index? - Which time intervals? - Time length of data? - Non-stationary; Beta estimates of a company change over time. How useful is the beta you estimate now for thinking about the future? - Betas change with a company's situation - Estimating a future beta; may differ from the historical beta - Beta is calculated and sold by specialized companies

CAPM Basic Assumptions

All investors: - Use the same information to generate an efficient frontier - Have the same one-period time horizon - Can borrow or lend money at the risk-free rate of return - No transaction costs, no personal income taxes, no inflation - No single investor can affect the price of a stock - Capital markets are in equilibrium

Security Market Line

Beta measures systematic risk: - Measures relative risk compared to the market portfolio of all stocks - Volatility different than market All securities should lie on the SML: - The expected return on the security should be only that return needed to compensate for systematic risk. - Required rate of return on an asset (ki) is composed of: 1. risk-free rate (RF) 2. risk premium (i [ E(RM) - RF ]) Market risk premium adjusted for specific security ki = RF +i [ E(RM) - RF ] The greater the systematic risk, the greater the required return

Capital Asset Pricing Model (CAPM)

Elegant theory of the relationship between risk and return; - Used for the calculation of cost of equity and required return - Incorporates the risk-return trade off - Very used in practice - Developed by William Sharpe in 1963, who won the Nobel Prize in Economics in 1990 - Focus on the equilibrium relationship between the risk and expected return on risky assets - Each investor is assumed to diversify his or her portfolio according to the Markowitz model

The Separation Theorem

Investors use their preferences (reflected in an indifference curve) to determine their optimal portfolio Separation Theorem: - The investment decision, which risky portfolio to hold, is separate from the financing decision. - Allocation between risk-free asset and risky portfolio separate from choice of risky portfolio, T. All investors: - Invest in the same portfolio - Attain any point on the straight line RF-T-L by either borrowing or lending at the rate RF, depending on their preferences

Market Portfolio

Most important implication of the CAPM - All investors hold the same optimal portfolio of risky assets - The optimal portfolio is at the highest point of tangency between RF and the efficient frontier - The portfolio of all risky assets is the optimal risky portfolio; called the market portfolio

The New Efficient Set

Risk-free investing and borrowing creates a new set of expected return-risk possibilities Addition of risk-free asset results in; - A change in the efficient set from an arc to a straight line tangent to the feasible set without the riskless asset - Chosen portfolio depends on investor's risk-return preferences

The Equation of the CML is:

Slope of the CML is the market price of risk for efficient portfolios, or the equilibrium price of risk in the market

How does adding a stock to an existing portfolio change the risk of the portfolio?

Standard Deviation as risk: - Correlation of new stock to every other stock Beta: - Simple weighted average - Existing portfolio has a beta of 1.1 - New stock has a beta of 1.5. - The new portfolio would consist of 90% of the old portfolio and 10% of the new stock - New portfolio's beta would be 1.14 (=0.9×1.1 + 0.1×1.5)

Portfolio Choice

The more conservative the investor the more is placed in risk-free lending and the less borrowing The more aggressive the investor the less is placed in risk-free lending and the more borrowing; most aggressive investors would use leverage to invest more in portfolio T