Vnu journal of Science: Policy and Management Studies, Vol. 3, No. (2017) 21-29



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4087-133-7713-1-10-20170719
Unit 1
4. Methodology and data 
The article uses the above indicated typical 
methods to evaluate the market concentration of 
Vietnamese mobile services in order to make a 
comparative analysis between Vietnam market 
with some other mobile markets in different 
countries. 
To calculate the market concentration index 
HHI , we can use the market share of mobile 
networks by subscription and by revenue. Due 
to the discontinuity of mobile operator revenue 
data over the years, this article uses 
subscription market share from [21] to calculate 
HHI. In HHI calculation, although Mobifone 
and Vinaphone are two different networks, 
before 2014, these two networks are either 
owned or controlled by VNPT, so the market 
share of the two networks is merged between 
2006 and 2013. In 2015 and 2016 the market 
share of these two networks is calculated 
separately.
For estimation of price elasticity of demand, 
the most commonly used model is in linear 
logarithms form (see [1, 15]): 
t
K
k
k
t
k
t
t
t
X
P
D









2
,
1
ln
ln
ln
Where 
t
D
is the service demand at time t, 
t
P
is the service price at time t, 
k
t
X
,
are the 
factors explaining the demand out of the price, 
such as per capita income, total number of 
subscription over time. 
The service demand is defined as the 
number of minutes of mobile calls, measured 
by taking mobile service revenue divided by 
average price. Revenue includes sales of 
various types of mobile services such as SMS, 
on-net, off-net, mobile generated calls as well 
as mobile termination services. The average 
price is constructed by taking the weighted 
average of the net prices, on-net and off-net, 
peak and low, and market share of network 
operators. Per capita income and Total 
subscription are used as explanatory variables 
with the assumption that as the income 
increases, 
demand 
for 
mobile 
telecommunications services increases; as the 
total number of subscription increases (due to 
non-price reasons), the demand for mobile 
telecommunications services increases. When 
estimating elasticity of demand model for the 
telecommunications market, it should be noted 
that prices and demands are not determined 
concurrently because markets are not perfectly 
competitive. Rates are usually determined in 
advance through the management of government 
agencies, after which demand will change 
accordingly, so the endogeneity problem may not 
be as noticeable as in the models estimated for 
other non-telecoms market. 
Data is collected from the statistics books 
on 
Information 
and 
Communication 
Technologies [21] and reports of the Vietnam 
Ministry of Information and Communication, 


 D.T.V. Duc, N.P. Hung / VNU Journal of Science: Policy and Management Studies, Vol. 33, No. 2 (2017) 21-29 
26
the Vietnam General Statistics Organization 
and the websites of service providers. The data 
is verified to ensure the consistence among 
different sources of data. Due to lack of data, 
the study only estimates the aggregate market 
model with data for 11 years, from 2006 to 
2016. In principle, to examine the ability of 
firm to change the market price (i.e. significant 
market power) the study needs to estimate the 
demand curve for each major firms doing 
business in the market. 
For model estimation, the least squares (OLS) 
method is used to examine the significance of the 
variables introduced and the two-stage least-
squares model (TSLS) is applied to correct the 
possible endogeneity problem. The resulting 
model together with the test values is shown in 
Table 2. Apart from price, statistically significant 
explanatory variable is Per-capita Income. 
Parameters in the model are consistent with 
theoretical predictions and statistically significant 
(T-tests). The F test for model simultaneous 
significance of variables and R2 parameters 
support the result model. 

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