City Size And Productivity:Evidence From Chinese Cities

China has entered a new era.China's economy has shifted from the stage of high-speed growth to the stage of high-quality development.Therefore,it is necessary to promote the quality,efficiency and dynamic changes of economic development.Among them,city efficiency has become the key content of city development.According to the principle of city economics,city agglomeration economy is one of the main driving forces of city production efficiency,and agglomeration economy is mainly divided into local economy and urbanization economy.Many economists have studied these two kinds of agglomeration economy,and found that agglomeration economy also has limitations.In the existing studies,it is a common practice to replace city agglomeration economy with city scale.By studying the relationship between city scale and city efficiency,we can find the driving force and influence of city agglomeration economy on city efficiency.City size in most developed and developing countries has grown steadily.However,after China's reform and opening up,the policy of "strictly controlling the scale of big cities,reasonably developing small and medium-sized cities and actively developing small towns" has been implemented.It was not until 2001 that China began to gradually relax the restrictions on the development of large cities and take the road of "coordinated development of large,medium and small cities and towns".Since 2001,Chinese cities have developed rapidly,which is mainly manifested in the rapid growth of City population,the rapid increase in the proportion of ity population to the total population,the rapid increase in the number of cities and the rapid expansion of the scale of cities.At the same time,city efficiency has also been greatly improved.Therefore,examining and demonstrating the relationship between city scale development and city efficiency with Chinese characteristics will help to find the optimal scale of city development in China and improve the quality and efficiency of economic development.Referring to the intermediate product models of Abdel-Rahman and Fujita(1990)and Pugua(2005)and Zhao Yao(2018),this paper refines the origin of innovation in the intermediate product model,puts forward the concrete form of innovation item,and takes effective labor force as the source of innovation item in the production function.At the same time,the Taylor series expansion method is used to enrich the city form,so that the city form in the model can represent all the city shapes,enrich the theoretical model of the relationship between city size and city efficiency,and strengthen the applicability of the intermediate product model in China's actual situation.Based on the panel data of 250 cities from 2001 to 2016,this paper studies the impact of city scale on city efficiency,and proves that there is an inverted U-shaped relationship between city scale and city efficiency.In addition,this paper also considers the spatial spillover effect between cities,and estimates the individual fixed effect by SDM model.The results show that the regional spatial spillover effect of city efficiency is significant.The city efficiency of adjacent cities will increase by 1%,and that of this city will increase by 0.451%.The relation curve between urban scale and urban efficiency in China is inverted U-shaped.There is an inflection point,that is,when the urban population is on the left of the inflection point,with the expansion of population scale,the urban efficiency will be greatly improved.When the population reaches the inflection point,the population reaches the optimal population scale,and the urban efficiency reaches the highest value.When the population exceeds the inflection point,the population scale will expand,Instead,urban efficiency will slow down.When the urban population is on the left side of the inflection point of the inverted U-shaped curve,it is necessary to continue to promote urbanization to improve urban productivity and urban efficiency;when a considerable part of cities are near the inflection point,the urban efficiency can reach the highest level;large cities beyond the optimal scale need to control urban norms to improve urban efficiency.