Has “The Outline of the Plan for the Reform and Development of the Pearl River Delta” Promoted to the Coordination of Guangdong-Hong Kong-Macao Greater Bay Area

The construction of the Guangdong-Hong Kong-Macao Greater Bay Area is an important regional development strategy implemented by our country in the new era. The development of coordination is the point. It is known that the scope of implementation of the outline includes the Pearl River Delta region and Hong Kong and Macao, consistent with the scope of Guangdong-Hong Kong-Macao Greater Bay Area. So, as to whether this outline has promoted the coordinated development of Greater Bay Area, this paper, based on the counterfactual analysis, constructs the HCW model and makes an empirical analysis from three aspects, regional economic relations, regional economic growth and regional economic differences. The results show that the outline did strengthen relations of Great Bay area, promote the regional economic growth and also have a positive effect on the reduction of regional economic differences. These conclusions can provide valuable reference for promoting the coordination of Guangdong-Hong Kong-Macao Greater Bay Area.


Introduction
In 2017, the Government Work Report of China has proposed "to formulate a Macao [1]. The main target areas of the Outline are the Pearl River Delta of Guangdong Province, including Guangzhou, Shenzhen, Zhuhai, Foshan, Huizhou, Dongguan, Zhongshan, Jiangmen and Zhaoqing. At the same time, the two special administrative regions of Hong Kong and Macao will be included in the planning in terms of development orientation and regional cooperation. It can be seen that the implementation scope of the Outline covers the Pearl River Delta, Hong Kong and Macao, which is completely consistent with the current geographical scope of the Great Bay Area. Therefore, in this paper, we will transform the "equivalent" of the Pearl River Delta area covered by the Outline into the Great Bay Area of Guangdong, Hong Kong and Macao in order to be consistent with the concept of the Great Bay Area currently proposed.
We believe that the experience of the Outline in promoting regional coordinated development is worth learning in planning and promoting the coordinated development of Great Bay Area. So, does the implementation of the Outline promote the coordinated development of Great Bay Area as planned? This is a problem that needs to be analyzed and evaluated scientifically.

Related Literature
Actually, about the effects of the outline, it has attracted the attention of many scholars. In the early stages of the outline, most of scholar study on it with qualitative analysis. For example, Yao Huasong and Xu Xueqiang, When interpreting policies, think that the new idea of the coordination of regional development is not fully integrated, which on the one hand, to promote the pearl river delta region in the areas of infrastructure, transportation, health care, social security, education and other public service facilities, on the other hand to keep local autonomy development, keep the local characteristic industry, local technology, the development of local cultural, protect the diversity of the local economy and society [2]. Ma Lindong, Xu Qiu believe that the key of regional economic cooperation of the Pearl River Delta is the degree of differences and complementary between the industry after the analysis of the outline from three different level-the international level, domestic level and the regional level. With the continued implementation of the outline, some scholars began to estimating the impact of the outline with method of quantitative analysis [3]. Peng Xijun made a quantitative evaluation of the process of industrial integration in the Pearl River Delta since the implementation of the outline by calculating the industrial isomorphism coefficient, regional specialization and location quotient. The results show that the degree of inter-regional engineering is rising, and the industrial layout is evolving towards specialization and differentiation [4]. In addition, Guo Fang and Song Yu made a quantitative analysis of the effectiveness of local government policy innovation since the implementation of the Outline, pointing out that local governments have achieved remarkable results in institutional policy, instrumental policy and objective policy innovation [5]. From the existing research literature, no literature has been found to evaluate the implementation effect of the Outline from the perspective of regional coordinated development.
As we all know, the evaluation of regional development strategy, planning and policy implementation is an urgent research work. However, the research in this area depends on the progress of methods. In recent years, most economists carry out policy evaluation based on the counterfactual framework [6] developed by Rubin. That is to say, man-made control groups, which do not exist in fact, are used as counter facts, to reflect the causal relationship between things through the difference between counterfactual and factual, so as to evaluate the policy effect. The common methods of constructing counterfactual frameworks include breakpoint regression (RD), double difference (DID) and propensity matching score estimation (PSM). The application of these methods is based on strict preconditions and assumptions. Among them, RD requires the same individual characteristics near the breakpoint [7]. This method is mostly applied in the field of labor and education economics. Among them, RD requires the same individual characteristics near the breakpoint. This method is mostly applied in the field of labor and education economics. DID has been developed by Card and Krueger and applied in empirical research [8]. This method needs to satisfy the premise of randomness, that is, the selection of treatment group and control group must be random and affected by common factors, and the degree of influence must be the same [9]. PSM needs to satisfy the strong premise hypothesis of "strong negligibility hypothesis" [10]. In addition to the above assumptions, the application of these methods requires a large amount of sample data. As far as the theme of this study is concerned, the impact path of policy implementation on economic linkages and development in the Great Bay Area is complex and diverse. Moreover, for different regions in the Great Bay Area, the impact degree is also different. In addition, the cities covered by the outline are not random decisions made by policymakers, and the data time series of implementation is also relatively short. Therefore, if we use the above counter-factual analysis methods to evaluate the effect of regional coordinated development of policies, it will have inevitable limitations.
Through reviewing the relevant literature, we find that the counterfactual analysis method developed by Hsiao et al. [11]. can effectively solve the problems of strong premise assumptions and insufficient time series data faced by methods above. Hsiao [12] and the impact of high-speed rail on the local economy [13]. They overcome the problems of missing variables and insufficient data in identifying and processing effects, and the results are robust. Therefore, this paper decides to use this method to evaluate whether the implementation of the Outline has promoted the coordinated development of Great Bay Area.
The rest of the paper is organized as follows: Section 2 discusses the counterfactual analysis method of regional coordinated development. It mainly constructs HCW model. Then, based on the data of cities in Great Bay Area from 1997 to 2015, the paper makes an empirical analysis of the coordinated development of Great Bay Area before and after the implementation of the Outline.

Counterfactual Analysis Method
In this section, according to the panel data evaluation method of Hsiao et al., we briefly introduce the counter-factual analysis ideas used to analyze the effect of regional coordinated development in the implementation of the Outline. ≠ ; and random error it u is independent of policy intervention variable it d condition with (3), we can see that the correlation of the individual on the cross section comes from these unobservable common factors t f : Therefore, the time series data 0 jt y of the control group before the implementation of the Outline can be used to fit the 0 it y of the treatment group, which can be expressed as: By estimating coefficients i α and * ij α and using the time series data ( ) of the control group after the implementation of the Outline, the estimated value of counterfactual Then, the net effect of the Outline on the region i covered is as follows: If it ∆ is stable, the average treatment effect (ATE) is as follows： where, T represents the end year of the evaluation of the policy effect of the Outline.
In order to minimize the prediction error, this paper uses methods of Hsiao et al. to construct the optimal control group [14]. That is, based on the adjusted R-square and Akaike Information Criterion (AICC), the best fitting ( ) 1 k k n ≤ ≤ regions were selected from n control groups to estimate the value 0 it y of counterfactual cases.

Data and Settings
As mentioned earlier, the main areas of implementation of the Outline are 9 cities in the Pearl River Delta region of Guangdong Province, but at the same time, in the Outline, the regional links and cooperation between the Pearl River Delta region and Hong Kong and Macao are emphasized. Therefore, the Pearl River Delta region and Guangdong-Hong Kong-Macao Great Bay Area are treated as two treatment groups when evaluating the impact of the Outline on the regional coordinated development. Based on the hypothesis of Hsiao et al. that individuals on the cross-section are driven by common factors, and considering minimizing the influence of regional heterogeneity, such as culture, climate and geography, this paper selected 9 other cities in Guangdong Province as the control group of the Pearl River Delta cities, namely Chaozhou, Jieyang, Maoming, Qingyuan, Shantou, Shanwei, Shaoguan, Yangjiang and Zhanjiang.
Regarding the selection of the control group between Hong Kong and Macao, this paper considers that although Hong Kong and Macao and the Mainland implement "one country, two systems", their economic development with the mainland is becoming closer and closer, and they have "common factors" of economic development. At the same time, considering that Hong Kong and Macao are the two windows through which the mainland of China connects with the world economic system, they are open to the outside world and have closer economic ties with the outside world, Therefore, the macro-environment and international environment of its economic operation also have the "common factors" needed to construct the control group. In order to select the best control group, this paper chooses 10 provinces and cities along the coast of China and 9 countries in Asia, Europe and the Americas to compare their GDP data with those of Hong Kong and Macao in the past 20 years, respectively. See Figure 1 and Figure 2.
As can be seen from the above Figure 1 and Figure 2, the development trend of Hong Kong and Macao is closer to that of the selected foreign economies.
Therefore, this paper holds that the economic operation of Hong Kong and Macao is more influenced by the international macroeconomic environment.  As mentioned above, this paper attempts to evaluate the regional coordinated development effect of the implementation of the Outline in the Guangdong-Hong Kong-Macao Great Bay Area. However, according to the existing literature, there is no unified criterion and evaluation method for regional coordinated development in academia at present. Most scholars evaluate regional economic coordinated development from one or several aspects, such as the degree of regional economic integration, regional division of labor, the degree of regional economic development gap or the speed of regional economic development [15] [16] [17]. Based on the concept of regional coordinated development defined by Qin Chenlin et al., which is "the coordinated development of regional economy refers to the process in which the economic links between regions become closer and closer, the economic interdependence deepens, the in-  sustainable development of the economies of all regions and the regional economic disparities tend to narrow under the conditions of regional opening up" [18], this paper measures regional coordinated development from three levels: regional economic links, regional economic growth and regional economic disparities.
Firstly, the gravitational model of spatial interaction is used to measure regional economic linkages. In the Pearl River Delta region, the successive development of highway, high-speed rail and urban rail makes the transportation convenience between cities continuously improve. Therefore, the traditional method of using spatial distance between two places in gravity model has been greatly limited. Considering that the modern transportation network is an important support for regional economic exchanges and cooperation, this paper uses the shortest distance between regions to correct the spatial distance in the traditional gravity model based on the high-speed road network and rail transit network. The specific formulas for calculating the degree of economic linkages where, i P and j P denote the total population of region i and region j at the end of the year; , i j GDP GDP denote the Gross Regional Product of region i and region j, and ij T denotes the shortest distance between region i and region j. By inquiring the opening time of expressways and rail transit in the Pearl River Delta region, ArcGIS 9.2 software was used to establish the database of urban node elements in the Pearl River Delta from 2008 to 2015, and eight 9 * 9 timedistance matrices were obtained by network analysis function. The regional economic linkages in the Pearl River Delta region are calculated by the following formula: ( ) The coordinated development of a regional economic entity requires the participation of all regions within it. One of the purposes of regional coordinated where, t CV represents the coefficient of variation of GDP growth rate among n cities in region in t Year, i y represents the GDP growth rate of city i, and y represents the average growth rate of n cities in the region. The larger the coefficient of variation is, the greater the relative difference of regional economic growth is, and the smaller the positive promoting effect of economic growth among regions is. On the contrary, the same is true.
For the measurement of regional economic disparity, the most widely used and mature methods are standard deviation, Gini coefficient, Theil index and so on. Because Theil index can divide the total differences into inter-regional and intra-regional differences, it can better reflect regional economic differences. In this paper, the Theil index is calculated by weighting the proportion of population and expressed by T.
where, i Y is the GDP of city i, Y is the total GDP of self-determination; i P is the population of city i, P is the total population of the region. The size of the Theil index reflects the size of regional economic disparity. The smaller the Theil index is, the smaller the regional economic disparity is.
As can be seen from Table 1 and Table 2, the fitting effect of control group  screened by AICC criterion is better, R-square is above 0.9. Therefore, we believe that the counterfactual situation after the implementation of the Outline can be predicted more accurately by the above optimal control group.

Result
Based on the counterfactual situation of the two basic indicators of real GDP and real per capita GDP, this paper calculates the three indicators of regional economic linkages, regional economic growth and regional economic disparities in the Pearl River Delta region and the Guangdong-Hong Kong-Macao Great Bay Area respectively after the implementation of the Outline. According to the calculation results, the paper analyzed whether the Outline had the effect of promoting the coordinated development of Guangdong-Hong Kong-Macao Great Bay Area.

Effects on the Coordinated Development of the Pearl River Delta
As mentioned above, the main target area of the implementation of the Outline is the Pearl River Delta region of Guangdong Province. Therefore, this paper first examines whether the implementation of the Outline promotes the coordinated development of the Pearl River Delta region. Figure 2 and Table 2 respectively reflect the actual situation and counterfactual situation of the Pearl River Delta region in three aspects: regional economic links, regional economic growth and regional economic disparities since the implementation of the Outline.

Effects on Regional Economic Linkages
To a great extent, the implementation of the Outline has promoted the economic links among cities in the Pearl River Delta region. As can be seen from Figure   3(1), after the implementation of the Outline, the economic links among cities in the Pearl River Delta region have been on the rise, with an average growth rate of 3.0%. Table 3 shows that the net effect of regional economic linkages   between cities to a greater extent.

Effects on Regional Economic Growth
From the net effects of regional economic growth in Figure 3(2) and column 7 of Table 3, it can be seen that, on the whole, the implementation of the Outline has a significant role in promoting economic growth in the Pearl River Delta region. It is worth noting that in the first year of the implementation of the Outline in 2009, the net effect of actual and counterfactual is still negative. After that, although the actual development trend of regional economic growth shows fluctuating characteristics, the actual growth of regional economy has been higher than the counterfactual situation without the implementation of the Outline since 2010, and the net effect continues to be positive, which shows that the implementation of the Outline is effective. It promotes the sustainable economic development of all regions in the Pearl River Delta region, and narrows the regional disparities in economic growth. This is an important manifestation of regional coordinated development.
The Outline puts forward the structural adjustment and upgrading require-

Effects on Regional Economic Disparities
Generally speaking, the implementation of the Outline has played a positive role in narrowing the economic disparities in the Pearl River Delta region. From the column 10 of Table 3, we can see that the net effect value of regional economic disparity is positive, and it increases continuously from 2009 to 2014, which shows that the implementation of the Outline has a positive impact on the reduction of regional economic disparity in the Pearl River Delta. Although the net effect decreased in 2015, it was still no less than 0.09. Therefore, it can be judged that the implementation of the Outline has played a more significant positive role in reducing the economic disparities in the Pearl River Delta region as a whole.  Kong-Macao Great Bay Area. Next, we will analyze the impact of the implementation of the Outline on the coordinated development of the Great Bay Area from three aspects: regional economic links, regional economic growth and regional economic disparities.

Effects on Regional Economic Linkages
From Figure 4(1) and Table 4, we can see that the overall effect of the implementation of the Outline shows that the average growth rate of regional eco-

Effects on Regional Economic Growth
From Figure 3(2), on the whole, the implementation of the Outline has played a positive role in promoting the economic growth of the cities in the Guangdong-Hong Kong-Macao Great Bay Area and narrowing the differences in the economic growth rate. As mentioned in the analysis above, under the influence of the Outline, 9 in 11 cities in the Great Bay Area have been restructuring and upgrading, and have maintained a good growth trend as a whole. The economic growth of Hong Kong and Macao relies heavily on the international economy. In recent years, the sustained downturn of international economic growth has had a greater impact on its economic growth. In addition, Hong Kong and the Pearl River Delta have declined in the "front store and back factory" model, Macao is limited to "gambling island", and the economic cooperation model of Guangdong, Hong Kong and Macao is also in the transition stage, which has affected the economic growth of Hong Kong and Macao to a certain extent. Therefore, it can be expected and understood that the actual curve of regional overall economic growth has slowed down in recent years. It is also noteworthy that, compared with the counterfactual situation, we can see that, except for the first two years of the implementation of the Outline, from 2011, the net effect value continued to be positive, with an average net effect of 0.0374. This shows that under the adverse external economic environment, the actual economic development and counterfactual development of the cities in the Great Bay Area have slowed down, But the Outline has promoted the economic growth of various cities in varying degrees and is conducive to narrowing the differences in their growth rates.

Effects on Regional Economic Disparities
From the comparison of Figure 3(3) and Figure 4(3), columns 8 -10 of Table 3 and Table 4, it can be seen that after joining Hong Kong and Macao for analysis, the regional economic disparity coefficient of the Great Bay Area has decreased.
Specifically, under counter-factual circumstances, the average value of the Pearl River Delta region is 0.02, and that of the Great Bay Area is 0.16. Under the implementation of the Outline, the Pearl River Delta area is 0.025, and t the Great Bay Area is 0.115. This is also in line with the reality, because most cities in Hong Kong, Macao and the Pearl River Delta still have large differences in the level of economic growth. In addition, it is worth noting that although the net effects of the Great Bay Area are negative, its growth rate of economic disparity indicators under the counter-factual circumstances has slowed down, while under the implementation of the Outline, the growth rate has an obvious upward trend, which is only 17.4% in 2014 and rises to 28.4% in 2015. This shows that although the Outline promotes the overall economic development of Guangdong-Hong Kong-Macao Great Bay Area, and narrows the regional economic disparities, its role is still limited.

Conclusions
This paper uses HCW model to analyze the impact of the Outline on the coordinated development of the Pearl River Delta and the Great Bay Area respectively from three aspects: regional economic linkages, regional economic growth and regional economic disparities. The main conclusions are as follows: First, the implementation of the Outline has significantly enhanced the economic linkages within the Great Bay Area and the Pearl River Delta. However, comparatively speaking, the impact on the former is less than that on the latter. Secondly, on the whole, the Outline has played a positive role in the economic growth of both the Great Bay Area and the Pearl River Delta, as well as in the reduction of economic growth among cities. Thirdly, the implementation of the Outline has no obvious effect on the narrowing of economic disparities in Guangdong-Hong Kong-Macao Great Bay Area, but it has played a positive role in promoting the narrowing of economic disparities in the Pearl River Delta.
The above three main conclusions show that, on the whole, the implementation of the Outline has a positive impact on the coordinated development of the Great Bay Area and the Pearl River Delta. In terms of strengthening regional economic linkages, the significant impact of the Outline deserves special attention. On the one hand, the strengthening of regional economic ties is an important prerequisite for achieving regional coordinated development. On the other hand, according to the analysis of this paper, the Outline strengthens the eco- dingyang Railway Bridge, all need to make scientific arrangements, so as to better play these projects to enhance internal economic ties of Great Bay Area.
In promoting regional economic growth, the implementation of the Outline has also played a positive role in the economic growth and the narrowing of Economic Growth Disparities among cities. It is noteworthy that the Outline has focused on promoting the structural adjustment and upgrading of the Pearl River Delta region. A new structure, with innovation as the driving force and advanced manufacturing and modern service industries as the main body, is being formed. Therefore, its role in the economic growth of the Pearl River Delta region and the reduction of economic growth among cities is more obvious. It can be predicted that the new industrial structure formed under the guidance of the Outline will surely lead to a new round of rapid economic growth in the Pearl River Delta region. The inspiration from this is that in the construction of the Great Bay Area, we still need to continue structural adjustment. For Hongkong and Macao, we should pay special attention to the adjustment of the structure to adapt to the great changes in the development environment brought about by the new technological revolution and the fourth industrial revolution and the construction of "one belt and one road".
In terms of reducing regional economic disparities, the Outline has no obvious effect on the narrowing of economic disparities in the Guangdong-Hong Kong-Macao Great Bay Area, but has a positive effect in the Pearl River Delta region. However, it is worth noting that its role in narrowing the economic disparities in the Great Bay Area is increasing year by year. Based on the above analysis, we believe that in the construction of the Great Bay Area, we should first strengthen the construction of the rapid transportation network and bring Hong Kong and Macao into the Pearl River Delta to strengthen their economic ties; second, we should overcome the obstacles caused by the "one country, two systems" to the connection between Hong Kong and Macao and the Pearl River Delta, and promote interaction and integration between them. Third, the Pearl River Delta region should continue to intensify its transformation and upgrading efforts to achieve more open and high-quality economic development, and gradually narrow the economic gap between Hong Kong and Macao at the per capita level.
In addition, the analysis of the Outline on promoting the coordinated development of Guangdong-Hong Kong-Macao Great Bay Area and the Pearl River Delta provides an empirical reference for the implementation of the Outline and the promotion of the coordinated development of the Great Bay Area, and also provides a positive case support for the theoretical construction of regional planning to promote the coordinated development of the region.

Conflicts of Interest
The author declares no conflicts of interest regarding the publication of this paper.