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CHAPTER SEVEN
THE PORTFOLIO SELECTION PROBLEM
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INTRODUCTION
• THE BASIC PROBLEM:– given uncertain outcomes, what risky securities
should an investor own?
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INTRODUCTION
• THE BASIC PROBLEM:– The Markowitz Approach
• assume an initial wealth• a specific holding period (one period)• a terminal wealth• diversify
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INTRODUCTION
• Initial and Terminal Wealth• recall one period rate of return
where rt = the one period rate of return
wb = the beginning of period wealth
we= the end of period wealth
b
bet w
wwr
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INITIAL AND TERMINAL WEALTH
• DETERMINING THE PORTFOLIO RATE OF RETURN– similar to calculating the return on a security– FORMULA
0
01
wwwrp
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INITIAL AND TERMINAL WEALTH
• DETERMINING THE PORTFOLIO RATE OF RETURNFormula:
where w0 = the aggregate purchase price at time t=0 w1 = aggregate market value at time t=1
0
01
wwwrp
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INITIAL AND TERMINAL WEALTH
• OR USING INITIAL AND TERMINAL WEALTH
where w0 =the initial wealth
w1 =the terminal wealth
01 1 wrw p
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THE MARKOWITZ APPROACH
• MARKOWITZ PORTFOLIO RETURN
– portfolio return (rp) is a random variable
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THE MARKOWITZ APPROACH
• MARKOWITZ PORTFOLIO RETURN– defined by the first and second moments of the
distribution• expected return• standard deviation
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THE MARKOWITZ APPROACH
• MARKOWITZ PORTFOLIO RETURN– First Assumption:
• nonsatiation: investor always prefers a higher rate of portfolio return
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THE MARKOWITZ APPROACH
• MARKOWITZ PORTFOLIO RETURN– Second Assumption
• assume a risk-averse investor will choose a portfolio with a smaller standard deviation
• in other words, these investors when given a fair bet (odds 50:50) will not take the bet
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THE MARKOWITZ APPROACH
• MARKOWITZ PORTFOLIO RETURN– INVESTOR UTILITY
• DEFINITION: is the relative satisfaction derived by the investor from the economic activity.
• It depends upon individual tastes and preferences• It assumes rationality, i.e. people will seek to
maximize their utility
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THE MARKOWITZ APPROACH
• MARGINAL UTILITY– each investor has a unique utility-of-wealth
function– incremental or marginal utility differs by
individual investor
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THE MARKOWITZ APPROACH
• MARGINAL UTILITY– Assumes
• diminishing characteristic• nonsatiation• Concave utility-of-wealth function
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THE MARKOWITZ APPROACHUTILITY OF WEALTH FUNCTION
Wealth
Utility Utility of Wealth
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INDIFFERENCE CURVE ANALYSIS
• INDIFFERENCE CURVE ANALYSIS– DEFINITION OF INDIFFERENCE CURVES:
• a graphical representation of a set of various risk and expected return combinations that provide the same level of utility
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INDIFFERENCE CURVE ANALYSIS
• INDIFFERENCE CURVE ANALYSIS– Features of Indifference Curves:
• no intersection by another curve• “further northwest” is more desirable giving greater
utility• investors possess infinite numbers of indifference
curves• the slope of the curve is the marginal rate of
substitution which represents the nonsatiation and risk averse Markowitz assumptions
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PORTFOLIO RETURN
• CALCULATING PORTFOLIO RETURN– Expected returns
• Markowitz Approach focuses on terminal wealth (W1), that is, the effect various portfolios have on W1
• measured by expected returns and standard deviation
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PORTFOLIO RETURN
• CALCULATING PORTFOLIO RETURN– Expected returns:
• Method One:
rP = w1 - w0/ w0
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PORTFOLIO RETURN– Expected returns:
• Method Two:
where rP = the expected return of the portfolioXi = the proportion of the portfolio’s initial value invested in security iri = the expected return of security iN = the number of securities in the portfolio
N
tiip rXr
1
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PORTFOLIO RISK
• CALCULATING PORTFOLIO RISK– Portfolio Risk:
• DEFINITION: a measure that estimates the extent to which the actual outcome is likely to diverge from the expected outcome
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PORTFOLIO RISK• CALCULATING PORTFOLIO RISK
– Portfolio Risk:
where ij = the covariance of returns between security i and security j
2/1
1 1
N
i
N
jijjiP XX
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PORTFOLIO RISK
• CALCULATING PORTFOLIO RISK– Portfolio Risk:
• COVARIANCE– DEFINITION: a measure of the relationship between two
random variables– possible values:
» positive: variables move together» zero: no relationship» negative: variables move in opposite directions
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PORTFOLIO RISK
CORRELATION COEFFICIENT– rescales covariance to a range of +1 to -1
where
jiijij
jiijij /