The means of increasing factor input to drive economic growth has been recognized as unsustainable. Because total factor productivity (TFP) represents the contribution of technological progress and efficiency improvement to economic growth, it is regarded as the core indicator of the quality of China's economic growth. World Bank in
The Research Report "China in 2030" believes that in order to overcome the "middle-income trap", China needs to focus on TFP to drive economic growth ＼ [1 ＼].
To improve the total TFP of the country, in addition to improving their own TFP in each region, improving TFP through regional cooperation is another important path. However, due to the current regional economic structure of "economic separatism" caused by "administrative separatism", "urban-rural separatism" and "factor separatism", under the intervention and influence of local governments on the economy, the economic dynamic mechanism of interregional cooperation is insufficient, which actually stays superficial, and regional competition is greater than regional cooperation. This has led to a series of consequences: (1) Hu Xiangting and Zhang Lu believe that this economic separation is an important factor leading to the convergence of regional industrial structure ＼ [2 ＼]. (2) Lu Ming and Chen Zhao believed that China's economic growth fell into the dilemma of market segmentation between provinces ＼ [3 ＼]. (3) Sun Xiaohua and others found through empirical research that local protectionism hindered the improvement of regional specialization ＼ [4 ＼].
The above studies have respectively revealed many problems caused by the existence of non cooperation in the region, such as repeated investment, overcapacity, factors that cannot be reallocated in production, market price distortion, industrial upgrading difficulties and so on. These problems reflect the low quality of overall economic growth caused by non cooperation, and are obviously the damage of TFP growth.
However, even if we can realize the importance of regional cooperation, it is not a simple thing for the central government and local governments to promote regional cooperation through effective means. Liu Ruiming pointed out that the existing official promotion incentive model has led to the formation of industrial isomorphism, and further led to market segmentation and local protection. However, if this model is abandoned, the local government will lose its leadership over the economy, which is what the local government does not want to see ＼ [5 ＼]. In fact, the government green GDP assessment, which has been piloted since 2005, has been unable to be implemented nationwide for 10 years, and its implementation difficulties are evident. Therefore, it is necessary to further explore the dynamic mechanism of local government cooperation, taking into account local interests and the quality of overall TFP growth.
1、 Analysis on the dynamic mechanism of local governments' non cooperative attitude
According to the accounting method of solo residual method, TFP growth is actually the economic growth caused by the growth of non factor input. Its most basic connotation is technological progress and efficiency improvement. However, why local governments are keen on inefficient economic growth rather than TFP driven economic growth, and then adopt a non cooperative attitude in regional cooperation, this needs to find a theoretical explanation perspective.
First, there are rent-seeking opportunities. Young's view is that local governments can use the price difference between the depressed factor price and the elevated output price caused by government intervention to seek rent ＼ [6 ＼] in economic segmentation. Obviously, if there is an integrated unified market in which factors can flow and prices are determined by the market, local governments cannot achieve such a price difference result.
Second, the inconsistency of competitiveness. Yang Guoliang and he Yuanqing found through the game model that local governments with competitive advantages always tend to open the market, while governments with competitive disadvantages always prefer local protection ＼ [7 ＼]. Lu Ming and other analysts believe that backward regions do not join the division of labor system. Although they lose the current division of labor income, they can improve their position in the negotiation of distribution of division of labor income in the future ＼ [8 ＼]. According to these two interpretation ideas, due to the imbalance of regional economic development in China, there are a few regions with absolute competitive advantage, and most regions have adopted the strategy of local protection.
Third, initial condition path dependence. Some scholars believe that the political and economic structure of local governments before administrative decentralization has caused long-term impact, which is actually an idea of initial condition path dependence. Yin Wenquan and CAI Wanru pointed out that the high proportion of state-owned enterprises, industrial layout structure and huge administrative institutions have created the motivation of local protection [9 ＼]. Lin Yifu and Liu Peilin believed that local protection and market segmentation were a continuous extension of the "catch-up strategy" of giving priority to the development of heavy industry in the early macro-economy [10 ＼]. These two views essentially reflect the long-term impact on the real economic structure and power arrangement due to the early excessive intervention of the government in the economy.
Fourth, there are non cooperative political and economic incentives. Zhou Li'an used the political promotion game to illustrate that under the zero sum game of official promotion, the "Officialdom" competition logic led local government officials to refuse inter regional cooperation ＼ [11 ＼]. The empirical research of Lu Ming and Chen Zhao shows that market segmentation is indeed conducive to the economic growth of the region itself for the time being, but there is an inverted U-shaped inflection point, which will eventually hinder the overall economic interests ＼ [3 ＼]. These two analytical viewpoints, which are based on political and economic interests respectively, show a prisoner's dilemma like development model among China's regional economies, that is, if only based on their own interests, regional non cooperation will be a priority.
2、 Mechanism of total TFP damage when local governments adopt a non cooperative attitude
Based on Chenery's decomposition method ＼ [12 ＼], we can express the accounting method of total TFP as follows:
TFPG=∑iYiY × Ai（t）? Ai（t）+1Y∑iLi? （fLi-fL）+1Y∑iKi? （fKi-fK） （1）
The subscript i in the formula represents each region, tfpg, y, AI, l and K represent total total total factor productivity growth, output, total factor productivity, labor and capital of region I respectively, FK and FL are total marginal capital productivity and total marginal labor productivity respectively, and FKI and fli correspond to the situation of region I. The second and third items on the right side of the formula show that if labor and capital flow to regions with higher marginal productivity, it will lead to the contribution to the total TFP, which means the harm of market segmentation. The first item AI on the right of the formula represents the total factor productivity progress of region I itself, which comes from technological progress and efficiency improvement. Formula (1) clearly explains the contribution of promoting factor flow through regional cooperation to the total economy, that is, the effect of factor reallocation, but other explanations are vague. The following formula constructed by kumbhakar ＼ [13 ＼] provides a more specific decomposition:
TFPG=FTP+TE+AE+SE（2）
On the right side of the formula: (1) FTP is the frontier technological progress, ftp=lnf (?)/ t. Where f (?) It is a production function and represents the TFP growth that can be promoted by the progress of cutting-edge technology. Since technological progress comes from regional R & D and technological diffusion in more developed regions, it is obvious that if regional cooperation, developed regions do not implement technological blockade, so as to spread technology to backward regions, it will be conducive to the growth of total TFP. (2) Te represents the technical efficiency, reflecting the gap between the actual output and the ideal maximum output under a given technical level (that is, the gap between the actual output and the frontier production function output). Its setting form is te=-du/dt, and u is the efficiency parameter. Its significance in regional cooperation is reflected in: if there is universal industrial isomorphism in the region and the frontier production function is at a low technological level, then this kind of production knowledge and economic structure are similar, on the one hand, the technical efficiency will be similar, on the other hand, due to the impact of the low technological level, the actual output is close to the ideal output, which represents the limited growth potential of TFP. On the contrary, if backward regions can cooperate with technologically advanced regions, TFP growth potential will be released as long as the absorptive capacity of technology and knowledge in developed regions is improved, even if the initial technological efficiency is low.
(3) AE represents configuration efficiency. AE=∑j（ λ j-Sj）x? j. Among them λ j= ε j/∑j ε j， ε J is the output elasticity of factor j input, λ J represents the relative output elasticity of factor j input, which reflects the relative contribution of factors, while SJ represents the relative cost share of factor j input, which reflects the relative level of factor costs. xj? Represents the growth of factor J. Its significance in regional cooperation is reflected in: in the case of economic separation, due to the deviation between factor contribution and factor price, it will hurt the growth of total TFP. At this time, if the region implements market integration and makes the market mechanism of price operate normally, it will ultimately be conducive to the growth of total TFP.
(4) Se represents economies of scale. SE=（RTS-1）∑j λ jx? j. Where rts= ∑ J ε j. Obviously, if rts>1, that is, in the case of economies of scale, increasing factor input in the same proportion will promote the growth of TFP. On the contrary, if rts<1, in the case of uneconomical scale, the increase of factor input will damage the growth of TFP. Its significance in regional cooperation is reflected in the following: it is very necessary to coordinate the development quantity and scale of industries in the development of various regions, especially to curb the continuous investment in industrial projects that are already in an uneconomical state of scale.
3、 The dynamic basis and necessity of using fiscal expenditure coordination mechanism to promote total TFP growth through regional cooperation
In this part, this paper will discuss how the fiscal expenditure coordination mechanism can promote regional cooperation, so as to promote the dynamic basis of total TFP growth, and the necessity for the fiscal expenditure coordination mechanism to play a role in it.
（1） The imbalance and complementarity of regional economic structure is the necessary basis for establishing a fiscal expenditure coordination mechanism
The imbalance and complementarity of regional economic structure is an objective problem. First, the regional economic structure has a strong path dependence, and the transformation of economic structure often faces high transfer costs; Second, China's regional labor factors reflect the characteristics of a very strong industrial structure. The significant differences in their cultural education and knowledge levels reflect great difficulties in the combination of labor factors and technical factors in the process of upgrading the economic structure; Third, affected by intellectual property rights and trade barriers, the diffusion and agglomeration of industrial structure and economic factors show strong spatial economic characteristics. The above three points make the growth of different economic structures show great differences. For economic regions with low-end economic structure, the problem of low-end economic structure often becomes the "trap" of economic growth in developing countries or regions. Even if the input of production factors is significantly increased, it is impossible to make the economy grow significantly. However, economic regions with high-end economic structure seek regional cooperation from expanding commodity markets and supporting basic industries, but often because of the lack of interest protection mechanism, they set up various technical barriers to maintain competitive advantage, thus lacking the real regional cooperation relationship.
Starting from this logic, there are two policy implications for the construction and improvement of the fiscal expenditure coordination mechanism: first, the coordination of fiscal expenditure should be pre emptive, that is, before regional cooperation, there should be certain policy layout considerations for regional economic development itself. For example, the fiscal expenditure should strengthen the investment in culture and education, and reduce the productive investment in the low-end economic structure for major cross regional infrastructure projects, so as to lay a cooperative foundation for regional trade, industrial transfer and technology diffusion. Second, the coordination of fiscal expenditure should be delayed, that is, once regional cooperation occurs, due to the loss and income of cooperation, the benefit distribution and guarantee mechanism should be coordinated through vertical and horizontal fiscal expenditure, such as the allocation of public goods investment in regional cooperation, and the coordinated arrangement of entry and exit of industrial structure development, so as to maintain cooperation.
（2） The coordination mechanism of fiscal expenditure is the driving force of regional cooperation with the goal of total TFP growth and the key to stable cooperation
As described in the first part of this paper, there are many non cooperative dynamic mechanisms in the region, which leads to two serious problems: market segmentation and industrial isomorphism. Fiscal expenditure coordination mechanism is an important way to solve the problem of regional non cooperation.
Hypothesis: if the Chinese region forms a regional cooperation body composed of I, J ∈ s, s= (1, 2... N), the regional cooperation body is composed of regions with different technological potential differences, and realizes market integration.
Proposition 1: the necessity of fiscal expenditure coordination mechanism exists in regional cooperation with the goal of total TFP growth.
Certificate: use Δ Tfpji said that the TFP increment (from the benefits of market integration and technology diffusion) generated by the local government J in the alliance after the local government I joined the alliance would be greater than each other's TFP growth, so that the alliance could be established.
In reality, the contribution of one party is directly obtained by the other party, but the loss of one party is directly borne by itself. If there is no vertical transfer payment of central finance or horizontal financial transfer payment between local governments, the cooperation cannot be completed.
Proposition 2: in the regional cooperation with the total TFP growth as the goal, there is the necessity of the fiscal expenditure coordination mechanism in the choice of regional cooperation mode.
Certificate: the TFP calculated by Solow residual method can be expressed by the following formula:
TFPG≈ln（Yt/Yt-1）- α ln（Kt/Kt-1）-（1- α） ln（Lt/Lt-1）（3）
The first item on the right of formula (3) reflects economic growth, and the second and third items on the right represent the growth of input factors. The formula represents that the growth of total TFP is actually a part of economic growth, but excluding factor growth, which means that if the cooperation between regions takes the growth of total TFP as the goal, it cannot be limited to the total economic growth, which is different from the cooperation mode of factor growth. Combined with the significance of formula (3) and the analysis of formulas (2) and (3) in the second part of this paper, table 1 reflects that in the regional cooperation with the growth of total TFP as the goal, the fiscal expenditure coordination mechanism should match on the specific cooperation mode of the region through path selection, so as to promote the realization of the goal, that is, the proof of Proposition 2.
Table 1 impact of fiscal expenditure and regional cooperation mode matching on total TFP
Economic growth mode brought by regional cooperation
The form of regional cooperation - the way to affect the total TFP
The form of regional cooperation -- the matching correspondence of the path choice of fiscal expenditure
Cooperation mode with total TFP growth as the goal (1) regional cooperation between technological potential differences - technological progress brought by technological diffusion
For example, fiscal expenditure promotes the growth of regional trade and the transfer of industrial ladder by promoting the construction of infrastructure such as logistics and energy between regions where there is a technological potential difference between the East and the West
(2) Market integration cooperation with free flow of prices, products and factors determined by the market mechanism -- the improvement of resource allocation efficiency brought about by the market mechanism
For example, the construction of market integration in the form of economic belt and economic circle promoted by fiscal expenditure.
(3) Coordinated cooperation between economic form and industrial division of labor -- avoiding efficiency loss caused by vicious competition
For example, the regional dislocation development promoted by fiscal expenditure (such as the Chengdu Chongqing urban and rural overall planning pilot area, the Wuhan urban circle and the "two oriented society" pilot area of the Changsha Zhuzhou Xiangtan Urban Agglomeration, the Fujian Ecological civilization first demonstration area, the Dongting Lake Ecological Economic Zone and other specific regional development models), so as to avoid the emergence of vicious economic isomorphism
Regional cooperation mode aiming at the growth of production factors
Cooperation that only promotes the growth of production factors - does not affect TFP growth
For example, financial payment transfer without technological progress and efficiency improvement (such as financial subsidies for loss making state-owned enterprises in backward areas)
（3） Build the coordination mechanism of fiscal expenditure through alliance game, and finally realize the dynamic principle of regional cooperation with the total TFP growth as the goal
For the consideration of performance evaluation and safeguarding local interests, local governments have excessive competition in fiscal expenditure. Such fiscal expenditure, which lacks a coordination mechanism, not only develops the economy, but also causes serious convergence of industrial structure, so that the efficiency of fiscal expenditure has not become the core orientation of government fiscal expenditure, and unreasonable fiscal competition mode will inevitably lead to low efficiency of fiscal expenditure, As a result, the regional economic gap has further expanded and the total TFP growth has been lost. Therefore, in the case of non cooperative game, the optimization of individual rationality and individual decision-making may be efficient for the region, but may be inefficient for the whole.
In terms of governance and market structure, the coordination process of fiscal expenditure mechanism is a dynamic game process in which the central government, local governments, consumers and enterprises participate. The improvement of the social welfare of consumers and enterprises is the ultimate goal of promoting the game between the central and local governments. However, in the process of economic system transformation, the interests of various game players are not consistent. From the perspective of vertical relationship, solving individual rationality problems with administrative orders can not achieve the expected effect, because the central government is far away from the actual market, and due to limited information constraints and rationality, it is still unable to accurately arrange economic resources and information; And the vertical game of local governments to maximize their own interests also substantially offset some efforts of the central government. Therefore, the solution of interregional problems should rely mainly on improving the market and strengthening the horizontal relationship between regions, while the solution of vertical relationship is mainly to make up for the parts that cannot be realized by themselves. From the perspective of horizontal relations, as the representative of regional economy, due to the influence of individual rationality on group rationality, how to drive local governments to consider group rationality for cooperation is a big problem. American scholar Dommel put forward two cores of horizontal intergovernmental relations competition and negotiation in intergovernmental relations: "horizontal intergovernmental relations can be conceived as a system of equal power division dominated by the dynamics of competition and negotiation." ＼ [14 ＼] this reflects that the key to solving the problem of horizontal relationship lies in the establishment of negotiation mechanism.
Alliance game provides an analytical tool of group rationality, in which the design of interest distribution mechanism can be used as the core basis for the fiscal expenditure coordination mechanism to solve the problem of joint rational decision-making, which is conducive to clarify the arrangement of the above-mentioned complex vertical and horizontal power interests between governments when the total TFP is the growth target.
4、 Fiscal expenditure coordination mechanism based on alliance game analysis
In the previous analysis, it is pointed out that due to individual rationality and inappropriate intervention of central and local governments, the dual failure of market and government has resulted, which has affected regional cooperation and damaged the growth of overall TFP. Obviously, fiscal expenditure, as one of the core economic regulation means of two levels of government, if used in a coordinated and reasonable manner, can not only positively guide the industrial development between and within regions, but also reduce the transaction costs and open market losses borne by local governments, so as to promote the formation of factor circulation and market integration. Wu Ying and Su Hong proposed to coordinate regional economic development by adjusting and improving the horizontal and vertical transfer payment mode of fiscal expenditure [15 ＼]. However, the study has not further discussed the distribution of benefits and the direction and structure of transfer payment. This paper will discuss it concretely through the analysis of alliance game.
（1） Model setting
An alliance game b (n, V) is a convex joint game with a set of participants of N and a characteristic function of V, which satisfies the transferable utility game (TU). Here, it means that there are n local governments, whose set is represented by n={1, 2,..., n}, and any subset S of N represents regional cooperation bodies composed of different local governments. Convex game means that there is the following inequality relationship: for any s, TN, there is V (s) + V (T) ≤ V (s ∪ T) + V (s ∩ T), where V (?) Represents the characteristic function of regional cooperation.
Local governments in various regions form various forms of regional cooperation according to the TFP growth and TFP losses brought by cooperation, such as the eastern, Western and "East West" regional cooperation. For joining different regional cooperation, there is both TFP growth and TFP loss, which is determined by the different levels of regional economic development and the characteristics of industrial form and structure, so that the region has TFP loss caused by competitive disadvantage and factor loss. For simple analysis, it is assumed that there is no dynamic adjustment of local government policies of regional partners to non regional partners. The total change of the new utility of the new alliance except for the original independent utility of region I is as follows:
（2） Model establishment
1. Establishment of characteristic function
Considering the total utility of the regional cooperative body (according to the analytical expression of the alliance game, hereinafter referred to as the alliance) s, which is composed of the regional local governments of each member, the utility change caused by its cooperative game behavior is affected by three parts:
(1) If s and N-S form a whole alliance n, the total TFP increment generated by the cooperative behavior of each regional government J of the whole alliance for each regional government I in S is] J ∈ NTFP Δ ij;
(2) Since J in N-S does not join s, the TFP increment of s resulting in non cooperative loss due to j is PIJ;
(3) In addition, the initial quantity should also be considered. The utility of s regional cooperation includes the initial utility value before the cooperation of local governments
Consider the formula (4) in the setting after the non-s member I of the regional cooperation body joins s
3. Model analysis and Policy Significance
If the coordination mechanism of fiscal expenditure can consider the policy design according to the Shapley distribution value in advance and afterwards, then according to the composition of the calculated Shapley distribution value, combined with the characteristics of the regional economy itself, we can see that different forms of cooperation have a great impact on individuals.
The first tfpi0 of Shapley's allocation value structure is the initial TFP level without any cooperation between regional governments. If the tfpi0 value is small relative to the right residual term, local governments near this value are more likely to be attracted by the relatively large right residual term to form an alliance. Since Shapley value is not evenly distributed, and its increment mainly reflects the relative size of marginal contribution, it is easier for regions with large marginal contribution to form alliances after alliances. The policy significance of the above analysis is that for most backward regions, their tfpi0 value is often small, but there are two opposite situations: first, with the economic isomorphism of other regions to be cooperated, the regional cooperation space caused by economic isomorphism is limited, but the competition relationship is large, so their marginal contribution is also smaller, and their willingness to cooperate will be greatly reduced; Second, the economy is heterogeneous with other regions to be cooperated, and there is a trade complementary relationship, so its marginal contribution will also become larger, and its willingness to cooperate will be greatly enhanced. Therefore, the prior consideration of the fiscal expenditure coordination mechanism (before regional cooperation) should reflect the coordination of the division of labor and layout of regional industries. From the perspective of policy planning, priority should be given to dividing the backward regions into a large plate. Through the overall planning of fiscal expenditure and the strategy of coordinated development of plates, we should first solve the problem of economic isomorphism within the plate, promote the flow of factors and information sharing within the backward regions, promote the faster diffusion of technology and knowledge in regional cooperation complementary to trade, and realize the internalization of the spillover effect of fiscal expenditure, Make up for its own structure and resource problems, and improve the efficiency of fiscal expenditure.
The second term of Shapley value structure represents the growth of TFP when the region cooperates. Obviously, for the cooperation between local government I and any other local government J, as long as positive benefits can be formed, the larger the regional cooperation body is, the better according to the formula structure. However, the actual situation is often more complex. One of the situations that will violate the calculation results of Shapley value is that if the utility of regional local government officials is inconsistent with Shapley value, it will also affect the cooperation structure.
The above article has introduced the refusal of local government officials to regional cooperation caused by political game. Under this game, the GDP assessment under the fiscal decentralization system determines the incentive characteristics of local government officials, This has directly led to the deviation of local fiscal expenditure structure: first, the deviation of fiscal expenditure structure caused by the lack of regional coordination - the horizontal competition carried out by local governments in order to speed up economic growth has led to the massive transfer of government public expenditure from public services such as culture, education and health to productive inputs such as infrastructure, resulting in the deviation of government public expenditure structure; The second is the overlap of fiscal expenditure structure caused by the lack of regional coordination - resulting in serious investment duplication and excessive competition. All this requires that the utility function structure of officials must be reformed to realize regional coordinated fiscal expenditure. One possible way is to include Shapley value in the assessment index in some way. However, considering that the assessment method of calculating officials directly into Shapley distribution value may be too complex, it can also be considered to include alternative indicators positively related to regional cooperation, such as considering the growth of cooperation regional TFP brought by regional cooperation, It is regarded as the evaluation item of officials' political achievements, that is, the original GDP of local officials is investigated, and the overall TFP growth of the cooperation area is examined, and the weight between the two is reasonably allocated according to the cooperation contribution.
The sum of the first two items of Shapley value reflects the situation that there is regional cooperation but there is no benefit coordination mechanism, while the third item reflects the distribution of cooperative residual utility according to the cooperative contribution, that is, even if the two conditions in proposition 1 are greater than 0, the benefit compensation must be carried out according to the contribution distribution principle, which is the key for the fiscal expenditure coordination mechanism to solve the efficiency problem in regional cooperation afterwards (after regional cooperation). In the first case, if this item is positive, the region must allocate I according to the contribution of TFP growth in the third item, otherwise I will adopt the strategy of not cooperating with the whole region. On the contrary, if the second item is negative, it is necessary to compensate other regional governments according to the above allocation, otherwise the region will refuse to cooperate with I. At this time, the above benefit distribution process can be completed through the combination of horizontal and vertical fiscal revenue and transfer payment.
Specifically: first of all, from the perspective of vertical fiscal transfer payment, the central government can obtain the fruits of TFP growth of regional cooperation in the form of fiscal revenue, and then by introducing Shapley distribution value as the basis for distribution, it will compensate the interests of regions that contribute greatly to regional cooperation in fiscal transfer payment. Secondly, considering that the vertical fiscal transfer payment lags behind the local government's financial needs and market conditions, it is necessary to strengthen the horizontal fiscal transfer payment. In particular, we should build a "local local" horizontal fiscal transfer payment channel in terms of policies and channels, and encourage regions that benefit more directly to conduct horizontal fiscal transfer based on Shapley's distribution value in assisting labor factor migration, industrial ladder transfer and public investment for the purpose of regional economic cooperation to other cooperation regions. Finally, it is necessary for the central government to build an information platform for regional market integration, reduce the coordination cost between regions in terms of institutional arrangements, and make regional cooperation possible through the means of coordinating fiscal expenditure, so as to finally promote the growth of total TFP.
5、 Conclusion
This paper discusses why local governments prefer to adopt the extensive economic growth and economic separatist mode of losing overall TFP rather than the individual rational choice of regional cooperation. With the continuous economic development and reform, the initial relative conditions between some regions are changing, and the economic structure is also changing, which means that the market and economic factors leading to regional non cooperation are disappearing. However, the ice breaking and deepening of political reform may last for a long time. When the power arrangement of the central and local governments changes very slowly, it is necessary to adopt new institutional arrangements. Using the method of alliance game analysis, this paper discusses the interest motive mechanism and interest distribution mode of realizing regional cooperation, advocates realizing reasonable interest distribution by realizing the coordination of fiscal expenditure between the central and local, local and local relations, and bringing regional cooperation into the official evaluation mechanism to promote regional cooperation, so as to promote the flow of factors between regions and realize the reasonable arrangement of industrial structure, And then promote the growth of total factor productivity, and realize the improvement of the quality of China's economic growth and the long-term sustainability of economic growth.