Abstract
Using the Theil decomposition method, this study analyzes regional inequality in South Korea and finds the country’s regional income disparities have been growing over the past two decades. Further group-specific analyses using the between and within group decompositions provide the following findings: (1) the inequality between Honam and non-Honam has been declining, repudiating the claim that Honam has been discriminated against by other regions; and (2) discrepancies between Gangwon and other regions have been growing, which is more serious than the Honam case and which is a priority of this research. In line with this, Gangwon Province the 2018 Winter Olympics is expected to contribute to narrowing this gap. Lessons from the Japanese experiences with the 1998 Winter Olympics will be discussed.
Introduction
The relationship between economic growth and inequality has been addressed by many economists over a long time (Basu, 2000). Kuznets (1955) suggested the well-known inverted U-shaped curve, such that economic inequality increases and then decreases over time with a country’s growth. Williamson (1965) applied Kuznet’s finding at the regional level and showed that regional inequality had the same inverted U-shaped relationship with economic growth. On the other hand, Alesina and Rodrik (1994) found a negative relationship between inequality and growth using data on income distribution and land in several countries.
This paper is about regional inequality in South Korea, with reference to Gangwon Province and the Winter Olympics in 2018 as a booster for the region’s sustainable development. The country has been one of the “champions” of economic growth, with per capita GDP growth of 6% per year on average, which resulted in “tens-fold” increases in per capita GDP in the past 40 years. The accomplishments of the past four decades are “unmatched” in history (Barro, 2003).
How has this dramatic growth affected regional inequality in the country? Each country is heterogeneous in terms of history, political background, location, and land size, so each may show different patterns of regional inequality. For example, South Korea’s economic development policies over past decades have been biased toward Seoul and Busan, and the link between the two. These policies may have ignored other regions, which might have contributed to increased regional inequality.
This paper first examines the pattern of South Korea’s regional inequality, which is measured by differences in mean income among groups living in different provinces. One of the widely used methods in measuring regional inequality is the Theil Index, because it can be additively decomposed into within group inequality (W) and between group inequality (B). In many cases, the between group inequality (B) is the only available resource to measure regional inequalities, and thus, deserves particular attention.
In that light, this paper analyzes regional inequality and suggests the so-called decomposition method as an improved measurement to better capture the overall inequality. Based on Shorrocks and Wan’s conclusion (2005) that regional inequality increases as more groups are included and on Kanbur and Zhang’s observations (2005) on China, this paper re-groups the existing sub-regions of Korea, based on its political and geographical background, and examines how regional inequality has changed.
More specifically, this paper is interested in the decomposition between Honam and non-Honam and between Gangwon and non-Gangwon. 1 It is commonly believed that the Honam area, located in the southwest part of Korea, has fallen behind other regions for political reasons. Gangwon Province is also behind in the process of economic development mainly due to geographic reasons. Out of these two, this study put more emphasis on the case of Gangwon Province, as it has been excluded from the country’s industrialization for a long time due to its geographical isolation and has not received attention as a topic of academic study.
This paper has the following findings. Overall, regional inequality in Korea has grown over the past two decades. However, inequality between Honam and non-Honam has been reduced due to Honam’s industrial development and its decreasing population. Disparities between Gangwon and other regions have been growing, but the 2018 Winter Olympic Games, which will be held in this province, are expected to provide momentum for growth in the region. The impact of the Olympics on sustainable regional development will be dealt with in detail in this study with a case study of the Japanese experiences in connection with the 1998 Olympic Games in Nagano to shed new light on Korea’s blueprints for the 2018 Olympics Games as well as the long-term sustainable development of the country’s lagged-behind mountainous region.
This paper is organized as follows. The second section conceptualizes regional inequality, with a focus on between group inequality, using the Theil Index. The third section discusses South Korea’s overall regional inequality. The fourth section provides results from decomposition analyses. The fifth section emphasizes the role and impact of the 2018 Winter Olympics on regional development. The sixth section concludes this research.
Regional inequality: conceptualization and decomposition
The rationale for preferring Theil’s T statistic is not that there is some inherent flaw with the other measures, but that Theil’s T has a more flexible structure that often makes it relatively more appropriate. If a researcher always had access to complete data at the individual level, then measures like the coefficient of variation or the Gini coefficient would usually be sufficient for describing inequality. However, in reality, individual data are rarely available, and researchers are left to deal with aggregated data. In this case, Theil’s T statistic is often a more appropriate and theoretically sound tool (Inequality Project, 2008).
The following formulae reveal the algebra behind Theil’s T. While these particular equations use income as the variable of interest, Theil’s T can address any number of quantifiable phenomena. When household data is available, Theil’s T is
where n is the number of individuals in the population, yp is the income of the person indexed by p, and µy is the population’s average income. If every individual has exactly the same income, T will be zero. This represents perfect equality and is the minimum value of Theil’s T. If only one individual has all of the income, this represents the utmost inequality and is the maximum value of Theil’s T statistic.
If members of a population can be classified into mutually exclusive and completely exhaustive groups, then Theil’s T statistic is made up of two components, the between group element (B) and the within group element (W) (T = B + W), where
where i indexes the groups, pi is the population of group i, P is the total population, yi is the average income in group i, and µ is the population-weighted average income across the entire population. When aggregated data are available instead of individual data, B can be used as a lower bound for the population’s value of Theil’s T statistic.
However, B is generically smaller than T, and the proportion of B of T fluctuates; on average, the proportion is only 12% (Shorrock and Wan, 2005). Thus, the definition of ‘region’ needs to be better conceptualized to better capture the current status of regional inequality of Korea. Decomposition – regrouping regions – is one way of doing so. Shorrock and Wan (2005) said that the method of decomposition accounts for up to 78% of regional inequality in the case of China. Kanbur and Zhang (2005) also used decomposition and re-grouped China’s provinces into rural and urban areas. By doing so, they showed an improved pattern of B between rural and urban areas. Based on these studies, this paper analyzes the regional inequality of South Korea using various decompositions.
An interesting property of the Theil Index is that it is relative; ‘Total Theil’ is a between group inequality in terms of individual citizens, but is a total inequality in a decomposition, meaning that decomposed inequalities are now between group inequality in terms of Total Theil
Thus, the rates of B of Total Theil indicate what proportion of decomposed inequality explains total inequality, suggesting an idea as to how important these decompositions are. This approach was originally used in Kanbur and Zhang (2005) when they decomposed China into coastal and inland, and rural and urban areas. After measuring the Total Theil of Korea, this paper uses the decomposition methods and regroups South Korea (Honam and the rest, Gangwon and the rest, urban and rural) to better capture the regional inequality of the country.
Overall regional inequality in South Korea
Before we move on to South Korea’s regional inequality, let us focus on the growth pattern of its per capita GDP. Although it shows a steadily increasing trend, its rate plummeted in 1960, 1979, and 1997 as a result of economic instability, reflecting Korea’s modern history (Figure 1). Based on these three periods of instability, Korea’s modern era since 1945 can be divided into four time periods.
Per capita GDP and growth rate of South Korea.
The first period, 1945–1961, was when Korea became independent of Japan (1945), South and North Korea established separate governments (1948), and the Korean War occurred (1950–1953). Having been destroyed by the war, Korea had almost no industry or social infrastructure, and the main source for its GDP was foreign aid. At the end of this first period, president Rhee Syngman was ousted after a corrupt presidential election, and the country was thrown into chaos.
The second period is 1961–1979. In 1961, General Park Chunghee staged a military coup and took power as the leader of South Korea. President Park maintained strong government power, based on export-oriented policies. At this time, Korea experienced rapid economic development with an average growth rate of 8%. His assassination in 1979 resulted in chaos in South Korea, and General Jeon Doohwan replaced him through another coup.
In the third period (1979–1997), Jeon became president (1981–1988), followed by Roh (1988–1993), and Kim (1993–1998). Korea, during this era, hosted the Olympic Games (1988) and had a booming economy and stable growth.
The fourth phase (1997–present) began with an unprecedented financial crisis in which Korea’s financial system was devastated.
This paper focuses on the third and the fourth periods, because data on regional income at the provincial level began to be collected only in 1985. To analyze regional inequality of South Korea, this paper uses these regional per capita GDPs for the 15 sub-national regions (six metropolitan city regions and nine provinces; see Figure 2). There are 16 sub-national regions in South Korea, seven of which are metropolitan regions, including Ulsan. However, this city was not directly considered in this paper because it only became one of the metropolitan cities in 1997; data prior to this year would be lost if this city was included. Instead, this study indirectly considers this city by adding its GRDP and population to its surrounding province. Based on the per capita mean GDP of each region, overall regional inequality was measured using Theil’s T (more specifically, equation B in Section 2), which is shown as THEIL_T in Table 1.
Map of South Korea.
Total Theil and its decomposed portions.
Source: Author’s own calculations based on provincial-level GDP and population, collected from KOSIS (n.d.) www.kosis.kr.
Note: THEIL_T is the overall Theil Index; THEIL_H/T is portion of decomposed Theil between Honam and other regions of overall Theil, which is (THEIL_Honam/THEIL_T) × 100, THEIL_G/T is the proportion of decomposed Theil between Gangwon and other regions of overall Theil, which is (THEIL_Gangwon/THEIL_T) × 100.
The indices themselves do not mean anything generically. However, by comparing the different indices over time, we can examine trends in regional inequality. The overall Theil Index reveals that regional inequality of South Korea has, in general, increased over the past two decades, from 0.02 in 1989 to 0.033 in 2012. There had been a decreasing period since 1997 until the early 2000s; this seems to have been associated with the financial crisis in 1997 and its aftermath, which mostly hit the more opulent regions, such as Seoul and the other major metropolitan regions, where the financial industries are concentrated. Decomposition methods in the following section will be used to better explain this pattern.
Decomposed Theil
Honam and others
It is commonly believed that there has been discrimination against the Honam region, the southwestern part of Korea (5, 12, and 13 in Figure 2). Considering Korea’s modern political history, this belief is not groundless. Korea’s politics can be summarized as a conflict between the Yeongnam-based ruling party and the Honam-based opposition party. As shown in Table 2, ever since Park Chunghee took power by a military coup in 1961, South Korean presidents were all from the Yeongnam region, the southeastern part of the Korean peninsula (2, 3, 7, 14, and 15 in Figure 2) until Kim Daejung, originally from Honam, became president in 1998.
South Korea’s presidents and their hometowns.
Park’s economic development plan focused on the development of the Capital Area and Yeongnam, and the connection between the two. The Capital Area was the first target because it already had an accessible social infrastructure, required for developing industries. Additionally, many cities in Yeongnam, including Gumi, Ulsan, Pohang, Changwon, and Masan, were industrialized with a variety of heavy industries (e.g. electronics in Gumi, shipping in Ulsan, steel in Pohang). The Capital Area and Yeongnam were more closely interconnected when the Gyeongbu Expressway, the first highway in South Korea, was opened in 1970. In this process of economic development, however, there was less investment in the Honam area.
This region had also experienced political discrimination. For example, the proportion of high-ranking public officials from Honam working in the national government in the 1970s was only 13%, even though population in this region is approximately 30% (Jeon, 1990).
This became more serious in the 1980s when the proportion of high-ranking public officials in the national government originally from Honam dropped to 9.6% and the proportion of CEOs in government-funded companies who were originally from Honam was only 0.9% (Jeon, 1990).
Things improved when the Kim Youngsam’s administration, the first non-military regime, took office in 1993, followed by Kim Daejung in 1998, the first president in South Korea, originally from Honam. It is commonly believed that the discrimination against Honam disappeared in the 1990s, especially since 1998.
How did this history affect the regional inequality of Honam and other regions? A completely satisfactory answer is not possible because, before 1989, there is a lack of data; data on regional inequality was first released in 1985 and, in 1989, Gwangju was separated from Jeonnam Province to be considered an independent metropolitan unit. Working from the available data, this section analyzes the inequality between Honam and other regions of Korea since 1989. Given the historical background, the following hypothesis can be constructed.
Hypothesis 1: As discrimination against Honam has eased, the regional inequality between Honam and non-Honam has declined.
Instead of a formal proof of this hypothesis, this paper provides “smoking-gun” evidence. To investigate the hypothesis, this paper decomposes Korea into two parts: Honam and the rest of Korea, and measures the Theil Index between these two regions. For a better measurement, this study divides the decomposed Theil between Honam and others by overall Theil, shown in the first column in Table 1. Based on the relativity property of Theil Index shown in equation (3), the overall Theil can be referred to as T, while the decomposed one is B, and we get the ratio (B/T). The result, in percentages, is displayed in the second column of Table 1.
As this hypothesis predicts, the inequality between Honam and the rest of Korea has been decreasing. In fact, the decreasing was dramatic, from 24.3% in 1989 to 0.3% in 2012, suggesting that the per capita mean incomes in those two regions had dramatically been converging. The convergence was mostly achieved in the early 1990s and maintained in single digits since 1996, even below 1% for many years. 3
Two possible effects may explain this dramatic convergence: first, increasing total GDP, and second, a decreasing population in the Honam area. Because per capita GDP is total GDP divided by its population, these effects, combined together, may have resulted in the soaring per capita income level of the Honam region, narrowing the gap between Honam and the rest of Korea.
First, Honam’s total GDP, especially the output level in manufacturing sectors, did increase in past years. It is true that there were many Honam-friendly policies in the 1990s. For example, as shown in Table 3, almost all of national industrial complexes in Honam were opened in the 1990s and the 2000s, and the number of companies, the number of workers, and the volume of exports were all growing. In particular, exports more than doubled between 2001 and 2005.
Industrial complexes in Honam Area.
Note: The first table explains only national complexes and the second table includes both national and local complexes.
Additionally, the West Coast Highway, opened in 2001, connected major cities and industrial complexes in the Honam area, all the way to Seoul. Increasing volume of trade between Korea and China also benefited Honam’s growth. Korea is China’s third largest trading partner, following the United States and Japan, and, in 2014, Korea established a free trade agreement with China (China Daily, 2014). This fact was particularly favorable to Honam’s growth because of its geographical proximity to China, being located on the west coast of Korea.
Second, the decreasing population of Honam magnified the effect of increasing per capita GDP, contributing to the convergence between Honam and non-Honam. As shown in Figure 3, Honam’s population growth rate had always been lower than other regions, and it even recorded negative rates for many years.
Population growth rate: Honam and others.
Overall, Honam has made some industrial progress recently; an increasing number of industrial complexes were constructed and the number of companies, the number of workers, and the export levels all have grown, which contributed to increasing output level. Per capita output level has soared because population of the region has declined. Increasing output levels in manufacturing sectors despite a decreasing population also indicate that Honam’s manufacturing sectors became more and more capital intensive, requiring more output per labor or less labor per output.
Gangwon and others
Like Honam, Gangwon is another region that has been isolated in the process of economic development in South Korea. In some sense, this region may be more discriminated against than Honam. The discrimination problem in Honam has been at least a “well-known” issue among Koreans, and there have been several attempts to solve the problem. However, very little attention has been paid to Gangwon with respect to its lagging economic growth and, as shown in Table 1, the gap has been consistently growing, which is more serious problem than the Honam case and which can be a good rationale to be discussed in this section.
As shown in Figures 2 and 4, Gangwon Province is located in the northeast mountainous part of South Korea. Due to its geographical constraints, this province has lacked growth, in both industry and agriculture. As such, there are no major manufacturing industries in the province, and transportation networks have not been sufficiently provided in this region. For example, as shown in Table 4, highways passing through Gangwon Province (Yeongdong, Joongang, and Gyeongchun) were constructed relatively recently. Railways have lagged even further behind. The Korea Train Express (KTX) is the country’s first high-speed train system with a maximum speed of 200 miles per hour, opened in April 2004. It takes less than 3 hours from Seoul to Busan, and South Korea is now more closely interconnected because of this bullet train system. According to KORAIL (2014), regions where the KTX stops show rapid economic development, such as the $100b investment in Iksan Industrial Zone with 1800 new employees from 22 different companies, and the $20tr investment in the Cheonan-Asan Industrial Zone with 100,000 employees from Samsung Electronics. However, as shown Figure 4, the KTX does not stop in any part of Gangwon province. 4
Railway Map of Korea (Gangwon area: inside the circle).
Major highways in Korea.
Source: Korea Expressway Corporation.
Note: There are 23 highways in Korea, as of 2014. Only some are introduced here.
Based on the narrative above, the following hypothesis can be constructed. To test the hypothesis, this paper decomposes Korea into two parts: Gangwon and the rest, and measures the Theil between the two regions. Like the case of Honam, this study divides the decomposed Theil between Gangwon and others by overall Theil, shown in the first column in Table 1, which is (B/T) × 100, using the term in equation (3). The result is provided in the third column in Table 1.
Hypothesis 2: With less accessibility, industrial development in Gangwon Province is behind, and therefore, regional inequality between Gangwon and the rest of South Korea has remained high for the past two decades.
This result verifies that, unlike the Honam decomposition, there was a high level of income disparity between Gangwon and other provinces. Except for the 1997–1998 period where inequality was reduced relatively due to the direct shock of the financial crisis to the capital area, the proportion of the Theil between Gangwon and the rest has increased approximately eightfold, from 0.2% in 1989 to 1.6% in 2012. Given that the decomposition of Honam and non-Honam showed a converging pattern, it seem that the income disparity between Gangwon and non-Gangwon is a more serious issue.
The 2018 Winter Olympics for the regional development in Gangwon
Gangwon is one of the most lagging regions in Korea; its gross regional development product has been one of the lowest in the country (Table 5) and the rates of its GDP and population out of those for the entire country have been declining for the past two decades (Figure 5). Consistent with this, there has been a growing income gap between Gangwon and other regions in Korea, as discussed in the previous section.
Gross regional domestic product in Korea.
Source: KOSIS (n.d.) www.kosis.kr.
GRDPGangwon / GDPTotal and PopulationGangwon / PopulationTotal (%).
Pyeongchang, the host city of the Olympics, is actually a remote mountainous village, 200 km away from Seoul with a population of 43,622 in 2010 (Gangwon Statistics Yearbook, 2010), far smaller than the host cities of the Olympics for the past 12 years (Sochi (Russia, 2014), Vancouver (Canada, 2010), Torino (Italy, 2006), and Salt Lake City (United States, 2002)). Moreover, its financial sustainability is only 10%, which is the lowest in the province, and in the country as well (Gyeonggi Development Institute, 2011). Against this backdrop, the Korean government has provided a master plan to build almost everything from scratch, including sports facilities, transport networks, and large-scale accommodations. Massive constructions on sports facilities include ski jumping, tracks for bobsled and luge, and speed skiing slopes in the Pyeongchang Mountain Cluster, and an up-scale ice rink in the Gangneung Coastal Cluster. For transportation, a new highway and a high-speed railway are scheduled to be completed by 2017. Additionally, the current capacity is not enough to accommodate all the participants expected during the Olympics, so each cluster needs more accommodation.
This mega-investment, unprecedented ever in the region, will create a tremendous financial burden not only on the local government but also on the entire country. For example, skeptical views have arisen on building a high-speed rail rink, one of the main pledges in the bidding process, that carries people in 68 minutes from Incheon International Airport to Pyeongchang due to the nine billion USD construction cost (Wall Street Journal, 2012). What will be important in this context is the ex-ante coordination heave and ex-post impact on the sustainable regional development. Before the Olympics, the government should play a role as a coordinator for synchronized expansion and balanced growth in many related sectors. According to Rosenstein-Rodan (1943) and Murphy et al. (1989), this will create demand externalities across other sectors and will eventually result in the so-called “Big Push.” From game-theoretical aspects, this could be interpreted as multiple Nash Equilibria in a following coordination game.
As shown in Table 6, if all agents choose “don’t invest,” they gain nothing and if all of them choose “invest,” positive demand externality occurs across each sector. If one of them invests while the other don’t, the one who invests ends up making a loss because no other sectors are invested. In this scenario, the Nash equilibrium is made where nobody invests or they all invest; the former is the so-called poverty trap and the latter, industrialization. Moving the equilibrium from the former to the latter is made through the Big Push.
Multiple Nash Equilibria in a coordination game.
In a lagging region like Gangwon, it is very difficult to expect spontaneous demand externalities across several sectors. In this context, the Olympics in the region will come as a massive exogenous shock that will create the Big Push. Coordinated investment in sports facilities, transport networks (road, rail, and air), and tourism (e.g. accommodation) will be also important for the ex-post sustainable development in the region.
With regard to this, Japanese experiences before and after the 1998 Olympics in Nagano provide lessons for Pyeongchang. Interestingly, what the South Korean government is implementing recalls what Japan did exactly 20 years ago. After Nagano’s host of the Winter Olympic was determined in 1991 (whereas it was in 2011 for Pyeongchang), the Japanese government started to construct sports facilities as well as transport networks. Nagano Shinkansen was completed in 1997 (whereas it is scheduled to be completed by 2017 in Gangwon), and the Olympic Games were successfully held in 1998 (and 2018 for Pyeongchang).
To host the event in a remote mountainous area, Japan spent, in total, 290 million Japanese yen (57 million yen for facilities and 233 million yen for transport, like Shinkansens (high-speed rail lines), highways, and an airport, most of which were financed by issuing bonds (News1, 2012)). Given this financial burden, and unpredictable profitability due to remoteness and small number of population, it would be very difficult for a local government, a central government, or private companies to make voluntary and internal decisions for this kind of mega-investment. The current unprecedented investment to the region would not have been possible without an external shock, like hosting the Olympics. In fact, the plan of constructing Japan’s first Shinkansen (bullet train), connecting Tokyo and Osaka (Tokaido Shinkansen) was initiated by hosting Tokyo Olympic Games. As such, the opening of the Shinkansen was made at the same day as the opening ceremony of the Games, which was 1 October 1964.
Despite this tremendous financial burden, Nagano is using the infrastructure well; newly constructed facilities for speed skating, ice hockey, and short track are currently used by the local people. The high-speed railway was also a big contribution. The Nagano Shinkansen, connecting Takasaki, Gunma, and Nagano (117.4 km), completed in October 1997, only four months before the Olympics, cut the travel time between Tokyo and Nagano to 79 min from 3 hours (International Olympic Committee (IOC), 2013). This made access to this remote region much easier than before and attracted tourists from Tokyo. For example, situated right across the street from Karuizawa Shinkansen station, the Prince Shopping Plaza is Japan’s largest outlet and very crowded with shoppers. This area, coupled with Niigata, is also well known for skiing, and people can easily access several ski resorts within one hour of travel from Tokyo. This railroad is now connected to Hokuriku Shinaksen and extended even further to northwest to Kanazawa (and all the way to Osaka in the near future), attracting people not only from Tokyo but also from Osaka and the surrounding Kansai Area. This development would not have been possible without the initial investment prior to the Olympics.
Korea can not only gain lessons from the Japanese experiences, but also find possible ways to collaborate with them. The IOC unanimously approved the so-called 2020 Agenda, which is a reform package for the Olympics to reduce financial burdens. According to the IOC, track events, such as the bobsled, luge, and skeleton are little used after the Games and Torino has abolished these facilities due to the high maintenance costs. The IOC recommended relocating these events to Japan that already has these facilities, which will save $120m in construction and $5m for annual maintenance (Joongang Daily, 2014). However, this plan could not be achieved easily given the current political relations between the two countries and their colonial history. For this plan to gain a political consensus, there should be an equal amount of compensation to Korea. One option would be to share some part of the Tokyo Olympics in 2020, hopefully in Gangwon, which might create economies of scale for both countries. This will be a win–win strategy and will be a positive impact on the regional development in Gangwon, as well (Figure 6).
Cluster map of Pyeongchang Olympics.
Conclusions
For the past four decades, South Korea has experienced rapid economic growth. It was called one of the “East Asian Tigers,” and the World Bank (1993) even called its rapid growth a “miracle.” However, although the pie is getting larger, it is not necessarily equally distributed: the famous statement that Pareto efficiency does not guarantee equality can be applied here. National inequality and decomposed inequality fluctuate over time. Overall, regional inequality in Korea has grown over the past two decades. Decomposed inequality between Honam and non-Honam has reduced, but between Gangwon and non-Gangwon, the gap has become wider, which should be treated more seriously. As Basu mentioned (2000), a certain “coordination heave” is what is needed to overcome the regional income gap of a country, and government should focus on reaching this goal in the most “cost-effective” way. This is particularly important for the regional development for Gangwon in line with the government’s massive investments for the 2018 Winter Olympics. The Japanese experience is worthwhile to be shared and international coordination with Japan for the Olympics in both 2018 and 2020 could be considered.
As a follow-up research topic, I plan to quantitatively measure the income disparity between Nagano and the other area of Japan to test whether the Olympics in 1998 had significantly positive impact on the reducing the gap. This approach can be extended to other countries with similar experiences, as well. As another follow-up, seeking possibilities for market-based development strategy will be crucially important for the sustainable development; government should encourage, as bottom-up, private sectors and all related shareholders to participate it instead of topping down the agenda directly. All of these topics should be reserved for further studies.
Footnotes
Funding
The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the National Research Foundation of Korea Grant funded by Korean Government (NRF-2014019910).