Vnu journal of Science: Policy and Management Studies, Vol. 3, No. (2017) 21-29
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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. tải về 274.4 Kb. Chia sẻ với bạn bè của bạn:
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