Variance 81Total variance of the return on a security
Portfolio variance()2122(^21)
2
2
2
- 0
,
cov
J
J
P
P
N J
K
J
J
N J
J
M P
P
P
x
to
due
and
x
where
ε
ε
ε
σ
σ
ε
β ε
β
σ
σ
β
σ
∑
∑
===⇒=+ ==Single-period random cash flows: Factor models - SFM
22
22iM
iiε
σσ
βσ+=⇒