Capm
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Transcript of Capm
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The Capital Asset Pricing Model
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Learning Objec-ves
¨ The capital asset pricing model ¤ Expected return on equity, rE ¤ Cost of equity, kE ¤ The simplest and most widely used model for this computa-on
¨ The market porBolio ¨ Beta risk ¨ Note: The CAPM model uses expected, mean rates of return and variance over some planning period ¤ r and σ2 are used generically
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CAPM Equa-ons From Topic 4
)r -‐ ]·∙(E[r + r = ]E[r FMFE β
FM
FE
r]E[rr]E[rβ−
−=
t
t1t
t
t1t
tE S
S]S[ES
]SS[ES
]S[E]r[E−
=−
=Δ
= ++
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CAPM Equa-ons
)rr(Εβ r 1]E[S
S
k1]E[S
S
FMF
1tt
E
1tt
−][⋅ ++=
+=
+
+
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CAPM Expected Returns
¨ In topic 10 we wrote ¤ ri = rF + βi (rM – rF)
¨ Expected returns on the ith equity security: ~N(ri, σi)
¨ Expected returns on the market porBolio: ~N(rM, σM)
¨ Expected returns on a porBolio: ~N(rP, σP) ¨ Returns on the risk free security: rF , σF=0
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Market PorBolio
¨ As more risky assets are considered, the fron-er of op-mal porBolios expands
σP
rP
Increasing M
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The Market PorBolio
Finally all investable risky assets are included and the op&mal fron-er becomes the efficient fron-er
The market porBolio is the op-mal risky asset when all investable risky assets are included. The market porBolio weights are defined by the rela-ve total equity values (market capitaliza-ons) of the risky assets.
rF
rM
M
σM
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Market PorBolio Proxies
¨ Total Market PorBolio for U.S. stocks ¤ 46% of global market porBolio ¤ Wilshire 5000 or MSCI Broad Index
n ~6,700 stocks and 99.5% of U.S. equi-es n Capitaliza-on weighted n Mutual fund: VTSMX n ETF: VTI (3,607 stocks)
¨ Total World Market PorBolio Ex U.S. stocks ¤ 54% of global market porBolio ¤ VEU (2,197 stocks)
¨ Typical Market PorBolio for U.S. stocks ¤ S&P 500
n Mutual fund: VFINX n ETF: SPY
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Market PorBolio Proxies 9
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Market PorBolio Proxies 10
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The Market PorBolio
¨ The op-mal risky porBolio on the efficient fron-er given a risky free asset is the market por2olio, M ¤ The sum total of what all investors own must be op-mal ¤ Investors are ra-onal, have all available informa-on, have the same
investment horizon and sta-s-cal return es-mates, use mean-‐variance op-miza-on,
¤ More will be said on ‘ra-onal’ and ‘informa-on’ in topic 12 ¨ It is ra-onal for investors to hold the market por2olio as their risky
asset along with the risk free asset ¤ 54% VEU ¤ 46% VTI
All investable assets → All tradeable assets → Equity assets globally →
U.S. total stock market index → S&P 500 index
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Sharpe Ra-o and CML
¨ Capital Market Line (CML) connects the risk free asset and the market porBolio
σ
r
rF
M
CML SM
T
CAL ST
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Capital Market Line
rF
SM
SM = (rM – rF) / σM
Sharpe ra-o for market porBolio
Si
CML Market PorBolio rM
σM σi
Si = (ri – rF) / σi
Sharpe ra-o for asset i
ri CAL
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Deriva-on of the Beta Risk Factor
¨ Calculate porBolio variance ¤ Split into market propor-onal variance and firm specific variance
ij
M
1jji
M
1i
2P σwwσ ⋅⋅= ∑∑
==
)σσβ(βwwσijε
M
1j
2Mjiji
M
1i
2P ∑∑
==
+⋅⋅⋅=
2Mjiijijε
ijε2Mjiij
σββσσ
σσββσ
−≡
+≡
ij
M
1jji
M
1i
M
1j
2Mjiji
M
1i
2P wwww ε
====
σ+σββ=σ ∑∑∑∑
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Deriva-on of the Beta Factor
¨ Split
¨ Firm specific covariance is assumed zero. Split the variances and covariances
ij
M
1jji
M
1i
M
1j
2Mjiji
M
1i
2P wwww ε
====
σ+σββ=σ ∑∑∑∑
⎟⎟⎟
⎠
⎞
⎜⎜⎜
⎝
⎛σ+σ+
⎟⎟⎟
⎠
⎞
⎜⎜⎜
⎝
⎛σββ+σβ=σ ε
≠==
ε=
≠===
∑∑∑∑∑∑ iji
M
ij1j
ji
M
1i
2M
1i
2i
M
ij1j
2Mjiji
M
1i
M
1i
2M
2i
2i
2P wwwwww
Market propor-onal Firm specific
variance covariance variance covariance
∑∑∑≠==
ε=
σββ+σ+σβ=σM
ij1j
2Mjiji
M
1i
2M
1i
2M
2i
2i
2P ww)(w
i
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Deriva-on of the Beta Factor
∑∑∑≠==
ε=
σββ+σ+σβ=σM
ij1j
2Mjiji
M
1i
2M
1i
2M
2i
2i
2P ww)(w
i
22M
2i
2i iε
σ+σβ=σ
2MMiiM σββ=σ
2MiiM σβ=σ
2M
iMi σ
σ=β
2Mjiij σββσ =
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Systemic and
non-‐systemic
(firm specific)
risk
Systemic
risk only
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Deriva-on of the Beta Factor
2M
iMi σ
σ=β
)rr(rr FM2M
iMFi −
σ
σ+=
Sub into CAPM formula
2M
FM
iM
Fi rrrrσ
−=
σ
−
Price of risk
MiiMiM σσρ=σ
M
iiMi σ
σρ=β
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PorBolio Beta Deriva-on
2M
M
1iiMi
P
2M
Mi
M
1ii
P
2M
Mi
M
1ii
P
2M
MPP
2M
PMP
σ
)σ(wβ
σ
)r,cov(rwβ
σ
)r,rwcov(β
σ)r,cov(rβ
σσβ
∑
∑
∑
=
=
=
=
=
=
=
=
∑=
⋅=M
1iiiP βwβ
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-15.0%
-10.0%
-5.0%
0.0%
5.0%
10.0%
15.0%
-12.5% -10.0% -7.5% -5.0% -2.5% 0.0% 2.5% 5.0% 7.5% 10.0%
Security Characteris8c Line
β
εk
(rM – rF)
(r – rF)
SCL
Plot of Walmart vs. SPX excess returns from Jan 2001 to Nov 2005 β=.637 α=.0003
kFMF )rr()rr( ε+α+−β=−
)σN(0,~ε 2εk
0),(cor 1kk =εε +
Ordinary Least Squares Assump-ons
22M
2i
2i iε
σ+σβ=σ
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Security Characteris-c Line
α
εk
(rM – rF )
(r – rF )
β
β·∙(rM – rF )
(r – rF ) = β(rM – rF ) + α + εk
0]E[ε)σN(0,~ε
k
2εk
=
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CAPM Model
εk
β
β·∙(rM – rF )k
(r – rF )k
(rM – rF )k
• α assumed zero ex-‐ante • Excess returns only from taking β risk
• α may be non-‐zero ex-‐post • non-‐random excess returns from taking firm specific risk
• A random component of excess return will be present ex post
)rr()rr(:anteex FMF −β=−−
kFMF εα)rβ(r)r(r :postex ++−=−−
22M
2i
2i iε
σ+σβ=σ
2
iε2M
2i
2M
2i
2i
2M
2i2
σσβσβ
σσβR
+==
Yahoo Finance
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SML ex-‐ante
rF
TM
ri
βi
rM
βM β
r
CAPM with β as the horizontal coordinate According to CAPM, fairly priced assets lie along the SML
)rr(βrr1β
βrr
βrrT
FMiFi
M
M
FM
i
FiM
−⋅=−
=
−=
−=
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SML ex-‐post
rF
βi
ri αi
rF+βi(rM-rF)
According to CAPM if
αi < 0, the asset is overpriced and should be, shorted, or under-‐weighted (Ti < TM)
α i > 0, the asset is underpriced and should be bought or over-‐weighted (Ti > TM)
α i = 0, the asset is fairly priced according to CAPM (Ti = TM)
under-‐priced assets
over-‐priced assets
rj
-αj
rF+βj(rM-rF)
βj β
r
M rM
βM
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CAPM parameter interpreta-on
¨ A high posi-ve beta for an asset has the following interpreta-on. ¤ The asset will have large price swings driven by market, SPX, movements
¤ The asset will increase the risk in the investor’s porBolio ¤ The investor will expect a high return ¤ The asset will outperform in a rising market
¨ Various studies show that posi-ve alpha is open associated with ¤ Low β stocks
¤ High (value stocks)
¤ Small cap stocks ¤ High dividend yield stocks
EEB
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Implica-ons of CAPM
¨ The market price of risk is the same for all properly priced securi-es and porBolios
¨ Investors will choose to hold combina-ons of the market porBolio and the risk free asset
¨ The market porBolio is on the efficient fron-er ¨ Only systema-c risk is priced into an asset ¨ For an individual stock, the only risk that brings excess return is the risk that the stock contributes to the market porBolio.
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CAPM Model Assump-ons
Market Assump8ons 1. All assets globally are traded (can be shorted) and divisible 2. For every borrower, there is a lender & supply = demand 3. There is a riskless security 4. No taxes and transac-on costs 5. Investors are price takers 6. Assets returns normally distributed (characterized by two parameters) 7. All investors borrow and lend at the riskless rate Investor assump8ons 1. Ra-onal, risk averse and maximize expected u-lity of return 2. U-lity is perceived as risk adjusted return 3. Risk measured as standard devia-on of return 4. Single period -me horizon 5. Homogeneous sta-s-cal return expecta-ons
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Essen-al Concepts 27