Single Index Model
Assumptions of Single
index model:
·
The first assumption of single index
model is that the security return is affected by only one factor i.e systematic
risk.
·
The investors have homogeneous interest.
·
The investors hold security for fixed period
to estimate the risk and return on security.
Advantages
of Single Index Model:
·
With the help of this model the number of
input is decreases to calculate expected return on security.
·
The model helps to determine the
systematic risk and unsystematic risk on security.
·
It makes easier to calculate the expected
return of security.
Example:
Mr. Sharma has invested in a portfolio in which 4 different securities included
that is A, B, C and D. His friend Nikhil tells about some portfolio term like
alpha and beta which help him to determine the expected return of that
portfolio that is, the alpha of security shows the security return which is not
affected to market return and the beta of security shows the sensitivity of a
security in relation to market. So, Mr Sharma wants to know the alpha and beta
of his investment portfolio with the help of given weight of security in a
portfolio, alpha, beta of each security.
Security in a portfolio
|
Weight of security
|
Alpha
|
Beta
|
A
|
0.3
|
1.2
|
0.26
|
B
|
0.1
|
-1.56
|
1.38
|
C
|
0.4
|
2.69
|
0.52
|
D
|
0.2
|
0.78
|
1.98
|
Solution:
Alpha
of given portfolio:
αp
= Ʃni=1wiαi
=
0.3*1.2 + 0.1*-1.56 + 0.4*2.69 + 0.2*0.78
= 0.36 + (-0.156) + 1.076 + 0.156
=
1.436
Beta
of given portfolio:
βp = Ʃni=1wiβi
= 0.3*0.26 + 0.1*1.38 + 0.4*0.52 + 0.2*1.98
= 0.078 + 0.138 + 0.208 + 0.396
=
0.82
Example:
Mr. Verma wants to invest in portfolio which consists 6
securities are P, Q, R, S, T and U. But he doesn’t know how much risk factor
affect his portfolio return. So, he is not able to take a decision to invest in
that portfolio or not. You have to help him by calculating the portfolio risk with
the help of given information: (standard deviation of market return 16)
Security
|
Weight of security in portfolio
|
Alpha
|
Beta
|
Standard deviation of
error term( σ2ei)
|
P
|
0.1
|
-0.27
|
1.72
|
252
|
Q
|
0.2
|
2.25
|
1.20
|
495
|
R
|
0.1
|
1.87
|
0.47
|
125
|
S
|
0.3
|
1.64
|
0.33
|
652
|
T
|
0.2
|
0.99
|
1.89
|
322
|
U
|
0.1
|
-1.01
|
1.44
|
106
|
Solution:
αp = 0.1 * (-0.27) +
0.2*2.25 + 0.1*1.87 + 0.3*1.64 + 0.2*0.99 + 0.1*(-1.01)
= (-0.027) + 0.45 + 0.187 + 0.492 + 0.198
+ (-0.101)
=
1.199
βp = 0.1*1.72 + 0.2*1.20
+ 0.1*0.47 + 0.3*0.33 + 0.2*1.89 + 0.1*1.44
= 0.172
+ 0.24 + 0.047 + 0.099 + 0.378 + 0.144
=
1.08
Portfolio
variance: σ2p = β2p σ2m + Ʃni =1 w2i σ2ei
=1.082*162 + 0.12*252
+ 0.22*495 + 0.12*125 + 0.32*652 + 0.22*322
+ 0.12*106
= 1.1664*256 + 2.52 + 19.8 +1.25 + 58.68
+ 12.88 + 1.06
=298.60 + 96.19
= 394.79
Example:
From the above example find out the expected return of given portfolio if the
market return is 18%.
Solution:
Erp = αp + βpErm
Erp = Expected return of
portfolio
Erm = Expected market return
= αp
+ βpErm
= 1.199 + 1.08*18
=
20.639
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