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Economics 434
Theory of Financial Markets
Professor Edwin T Burton
Economics Department
The University of Virginia
Economics 434 – Financial Market Theory
Tuesday,
Tuesday,
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August
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2010
Tuesday,
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25, 2012
Tuesday,
August
25,
2009
Modern Portfolio Theory
Three Significant Steps to MPT
Harry Markowitz
Mean Variance Analysis
The Concept of an “Efficient Portfolio”
James Tobin
What Happens When You Add a “Risk Free Asset” to
Harry’s story
Bill Sharpe (Treynor Lintner, Mossin, etal)
Put Tobin’s Result in Equilbrium
The Rise of Beta
The Insignificance of “own variance”
Economics 434 – Financial Market Theory
Tuesday,
Tuesday,
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August
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21,2010
2010
Tuesday,
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25, 2012
Tuesday,
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25,
2009
Need Some Statistics
Mean, Variance, Covariance
Standard Deviation
Mean --- roughly means ‘average’
Variance – squared differences summed up
Covariance – two variable, take differences of each from their
means, multiply the differences observation by observation
Standard Deviation = Square Root of Variance
We will typically use normal distribution – but that is not
necessary. We could use other distributions
Economics 434 – Financial Market Theory
Tuesday,
Tuesday,
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2010
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Because of uncertainty, we need a
different utility function
Why not just expected value?
Instead, we use expected utility
What’s the difference?
Economics 434 – Financial Market Theory
Tuesday,
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i 1
Some Definitions
2 i 1
n
xi
x
x
x
n
i
n
n
2
= √ 2
n
x, y
x ( x) y ( y )
i 1
n
1,2
Economics 434 – Financial Market Theory
1,2
12
Tuesday,
Tuesday,
September
August
24,
21,2010
2010
Tuesday,
Sept
25, 2012
Tuesday,
August
25,
2009
Modern Portfolio Theory
Randomness
Construction of efficient
(best) portfolios
Harry Markowitz
Economics 434 – Financial Market Theory
Tuesday,
Tuesday,
September
August
24,
21,2010
2010
Tuesday,
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25, 2012
Tuesday,
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25,
2009
How Do You Create A Portfolio?
Try It with Two Assets
Mean
“X1”
“X2”
Where are the Portfolios That Can
Be Created from Just These Two
Assets ?
Standard Deviation
Economics 434 – Financial Market Theory
Tuesday,
Tuesday,
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August
24,
21,2010
2010
Tuesday,
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25, 2012
Tuesday,
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25,
2009
Back to the ½, ½ Portfolio
Mean of
X1
Mean of P
Mean of
X2
Economics 434 – Financial Market Theory
Where P = ½ [X1] + 1/2 [X2]
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2010
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2009
Variance of a Portfolio
with two assets
P2 = (P - P)2
n
= {1(X1- 1) + 2(X2 - 2)}2
n
Economics 434 – Financial Market Theory
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2010
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Tuesday,
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Variance – with two assets
2
P
2
{
(X
)
+
(X
)}
1
1
1
2
2
2
=
n
= { (1)2[X1 - 1]2 + (2)2[X2 - 2]2}
+ 212(X1 - 1)(X2 - 2)}
n
Economics 434 – Financial Market Theory
Tuesday,
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2010
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Variance with 2 Assets Continued
= {(1)2[X1 - 1]2 + (2)2[X2 - 2]2
n
+ 212(X1 - 1)(X2 - 2)}
n
Economics 434 – Financial Market Theory
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2010
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Variance with 2 Assets - Continued
= (1)212 + (2)222 + { 212(X1 - 1)(X2 - 2)}
n
= (1)212 + (2)222 + 212Cov (X1,X2)
= (1)212 + (2)222 + 2121,2
Economics 434 – Financial Market Theory
Tuesday,
Tuesday,
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2010
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Tuesday,
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2009
Variance with 2 Assets - Continued
= (1)212 + (2)222 + 2121,2
Recall the definition of the correlation coefficient:
1,2
1,2
12
= (1)212 + (2)222 + 2121,212
Economics 434 – Financial Market Theory
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Tuesday,
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2010
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Tuesday,
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25,
2009
Variance with 2 Assets - Continued
= (1)212 + (2)222 + 2121,212
where
1,2
1,2
12
What Happens if = 1?
Economics 434 – Financial Market Theory
Tuesday,
Tuesday,
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2010
Tuesday,
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Tuesday,
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2009
If = 1
(1)212 + (2)222 + 2121,212
becomes
= (1)212 + (2)222 + 21212
2P= (11 + 22)2
P= (11 + 22)
Economics 434 – Financial Market Theory
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2010
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If = 1
P= (11 + 22)
If 1
P (11 + 22)
Economics 434 – Financial Market Theory
Tuesday,
Tuesday,
September
August
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21,2010
2010
Tuesday,
Sept
25, 2012
Tuesday,
August
25,
2009
Back to the ½, ½ Portfolio
If = 1
Mean of
X1
Mean of P
Mean of
X2
Where P = ½ [X1] + 1/2 [X2]
1,2 = 1/21 + 1/22
Economics 434 – Financial Market Theory
Tuesday,
Tuesday,
September
August
24,
21,2010
2010
Tuesday,
Sept
25, 2012
Tuesday,
August
25,
2009
Back to the ½, ½ Portfolio
If 1
1,2 1/21 + 1/22
Mean of
X1
Mean of P
Mean of
X2
Economics 434 – Financial Market Theory
Where P = ½ [X1] + ½ [X2]
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Tuesday,
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2010
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If = 1
Then all the portfolios are here
Economics 434 – Financial Market Theory
Tuesday,
Tuesday,
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2010
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If 1
Then all the portfolios are here
Economics 434 – Financial Market Theory
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2010
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This Means the “boundary”of the possible portfolios
looks like this:
Economics 434 – Financial Market Theory
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This is very convenient
Mean
Maximizes
Utility
Standard Deviation
Economics 434 – Financial Market Theory
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The End
Economics 434 – Financial Market Theory
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2010
Tuesday,
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25, 2012
Tuesday,
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25,
2009