部门异质性替代弹性与产业结构变迁

Heterogeneous Sectoral Elasticity of Substitution and Structural Transformation

现有产业结构变迁文献主要基于恩格尔法则和Baumol效应解释产业结构变迁过程,而基于Baumol效应的模型往往被认为难以独立地刻画农业、服务业和工业三大产业部门完整的产业结构变迁事实。本文将复合CES函数引入到一个经典的Baumol效应模型中,允许农业与非农业之间、工业与服务业之间的替代弹性存在异质性,从根本上克服了现有基于Baumol效应模型的缺陷,还有潜力解释世界各国普遍发生的工业部门增加值占比先上升后下降的"倒U型"结构变迁过程。基于1978年以来的数据,本文发现仅仅依靠Baumol效应,就可以较好地模拟我国农业增加值GDP占比不断上升、服务业GDP占比不断下降和工业增加值GDP占比高位徘徊的基本经验事实,并且我国工业部门还未明确进入"倒U型"产业结构变迁后半段,因此现在还不能判断我国已经进入工业部门劳动力比重和增加值比重下降的"后工业化阶段"。

Kuznets facts summarize the empirical patterns of structural transformation over the process of development.As the income grows,the three broadly defined sectors behave differently:the GDP and employment shares of the agricultural sector shrinks;the share of the service sector grows;and the share of the industrial sector follows an inverted-U shape,that is,the share of the added value of industrial sector first rises and then falls is a common phenomenon in the structural change process of all countries in the world.Since the reform and opening-up,the Kuznets fact that the share of agricultural added value has been declining and the share of service industry has been rising in China’s agriculture,industry and service industry is established,but it remains to be seen whether the proportion of industrial added value has entered a declining stage.There are mainly two theories that try to explain the empirical patterns of structural change.The first one highlights the role of Engel’s law(the income effect)which argues that people tend to consume more goods with higher income elasticity.The second one relies on the Baumol effect(the price effect)which argues that resources are reallocated to sectors that grow slower(faster)if the elasticity of substitution among sectors is less(greater)than 1.Generally,Engel’s law is considered more important in explaining the structural change,while the existing literature based on the Baumol effect alone is not able to capture the entire pattern of structural change of the three sectors.For example,in a three-sector model,to describe the structural change process of factors of production flowing from the agricultural sector to the non-agricultural sector,it is necessary to assume that the technological progress rate of the agricultural sector is higher than that of the non-agricultural sector when the substitution elasticity among the three sectors is less than 1,which obviously cannot meet the empirical facts of most countries.If it is assumed that the substitution elasticity among the three sectors is greater than 1,then the factors of production will flow from the service sector to the industrial sector with faster technological progress,which violates the basic fact of the industrial structure change.The existing mainstream literature is based on Engel’s law to explain the"inverted-U shape"structural change process in which the proportion of industrial added value rises first and then falls.This paper constructs a three-sector industrial structure change model based on the Baumol effect,trying to describe the typical facts of the structural change of the agricultural sector,service sector and industrial sector,including the"inverted-U shape"structural change process of the industrial sector.Our main innovative approach is to allow heterogeneous substitution elasticity between agriculture and non-agriculture,and between industry and service sector.The classic literature based on the Baumol effect uses the symmetric Elasticity of Substitution(CES)function.No matter how many industrial sectors exist in the model,the substitution elasticity between any sector must be the same.Because of this limitation of symmetrical CES function,the multi-sector model based on it is mainly suitable for explaining the process of industrial structure change of two sectors.We calibrate the parameters of our theoretical model with the Chinese data from 1978 to 2016.The calibrated model can match the entire process of structural transformation of the three sectors in China during this period.Our quantitative results show that this model can explain the Kuznets fact that the ratio of agricultural added value GDP continues to decline and the ratio of service added value GDP continues to rise,and it can also explain the basic fact that the ratio of industrial added value GDP has been hovering at a high level for a long time.A set of numerical experiments show that increasing the substitution elasticity between agriculture and non-agriculture and reducing the substitution elasticity between industry and service industry can greatly improve the fitting effect of the industrial structure change process of the three major departments in China,and at the same time,it can fit the"inverted-U shape"industrial structure change process in which the industrial proportion first rises and then falls.We contribute to the literature on multi-sector growth and structural change by allowing for heterogeneous sectoral elasticity of substitution in the standard structural change model with homothetic preferences.This feature enables our model to generate the"Kuznets fact"and"inverted-U shape"industrial sector structural change process in the structural change model without income effect.To sum up,we develop a dynamic general equilibrium model of structural change with heterogeneous sectoral elasticity of substitution to show that the Baumol effect alone can explain structural change and use this model to account for the structural change in China.We find that allowing for heterogeneous sectoral elasticity of substitution can explain structural change and can quantitatively match the structural change in China.Our finding also implies that China’s manufacturing sector has not entered the second half of the"inverted-U shape"industrial structure change,so it cannot be judged that China has entered the"post-industrialization stage"where the proportion of labor force and added value in the industrial sector decreased.