Variance 87
Total variance of the return on a security
Portfolio variance
()
2
1
2
2
,
1
,
2
2 1
2
1
,
2 1
2
1
,
2
*
0
,
cov
*
...
J
J
P
P
N J
K
J
Fi
J
N J
J
Fi
P
F F P F F P P
x
to
due
and
i
all
for
x
where
ε
ε
ε
σ
σ
ε
ε
β
β
σ σ β σ β σ
∑
∑
=
=
=
⇒
=
=
+
+
+
=
Single-period random cash flows: Factor models - MFM
2
2 2
2
2
,
2 1
2
1
,
2
...
i
F
Fi
F
Fi
i
ε σ σ β σ β σ
+
+
+
=
⇒