2007 Annual International CHRIE Conference & Exposition
146
than the less high growth rate of Japan (e.g., 4.08 percent), which indicates that Singapore is a much more important
market
than Japan, despite its small market size. In reality, however, Japan, which generates more arrivals (return),
should be treated more importantly. In other words, the optimal solutions are decided purely by the variance-
covariance combination of growth rate, assuming that the number of arrivals from countries is almost the same.
Thus, using the growth rates may lead to erroneous solutions for Taiwan. Therefore, the study decided to use the
number of arrivals to Taiwan for individual countries (markets). The weight of each individual
market within the
portfolio also will play an important role in determining the overall arrivals. First of all, the expected return (mean
arrivals) of a portfolio comprising
n
markets is the weighted average of the expected return of each market in the
portfolio:
( )
( )
∑
=
=
n
i
i
i
p
r
E
w
r
E
1
,
(1)
, where
( )
p
r
E
: the expected return of
the portfolio,
w
i
: the proportion of market
i
in the portfolio,
( )
i
r
E
: the
expected return on market
i
,
n
: the number of markets in the portfolio.
Second, the variance of returns of the portfolio depends on the variance and covariance of markets in the
portfolio. For the case of a two-market portfolio, the variance of the portfolio returns can be expressed as:
( )
(
)
2
1
2
1
2
2
2
2
2
1
2
1
2
,
2
r
r
Cov
w
w
w
w
r
Var
p
p
+
+
=
=
σ
σ
σ
,
(2)
, where
( )
p
r
Var
: the variance of returns of the portfolio,
2
i
σ
: the variance
of returns of market
i
,
(
)
2
1
,
r
r
Cov
: the
covariance of returns between markets 1 and 2, which measures the extend to which returns of markets 1 and 2
move together,
(
)
2
1
12
2
1
,
σ
σ
ρ
=
r
r
Cov
,
12
ρ
: the correlation coefficient between returns of markets 1 and 2,
1
w
and
2
w
: the weights of markets 1 and 2 respectively, where
0
1
≥
w
and
0
2
≥
w
and
1
2
1
=
+
w
w
.
When
(
)
0
,
2
1
=
r
r
Cov
, returns of markets 1 and 2 are uncorrelated. It is obvious that the variance of the portfolio
returns would be:
( )
2
2
2
2
2
1
2
1
σ
σ
w
w
r
Var
p
+
=
.
(3)
Since
1
0
1
≤
≤
w
and
1
0
2
≤
≤
w
, thus
1
2
1
w
w
≤
and
2
2
2
w
w
≤
. Accordingly, the variance of returns of the
portfolio would be less than the weighted sum of the variances of the individual markets. When
(
)
1
,
2
1
<
r
r
Cov
,
then the variance of the portfolio will be less than the weighted sum of the individual markets. Apparently, if the
arrivals from different markets are negatively correlated, the benefits (reduction in portfolio variance) from
diversification will be greater. When
(
)
1
,
2
1
−
=
r
r
Cov
(perfectly negative correlation), the
portfolio variance will
fall to zero.
To find all possible efficient portfolios, we need to calculate the expected arrivals and variance of each
market and the pair-wise covariance between markets. After we computed the expected arrivals and the
variance/covariance matrix, the problem is reduced to the optimization of a quadratic function subject to constraints.
The variance and expected returns of individual efficient portfolios can be calculated based on the following model:
Objective function: Min
( )
j
i
n
i
n
i
n
i
j
j
j
i
i
i
r
r
Cov
w
w
w
,
1
1
,
1
2
2
∑
∑ ∑
=
=
≠
=
+
σ
,
(4)
Subject to:
∑
=
=
n
i
i
w
1
1
(5)
( )
( )
p
n
i
i
i
r
E
r
E
w
=
∑
=
1
(6)