基于半参数随机成本前沿方法的道路运输企业成本无效率研究——以山西公路客运企业为例

Cost Inefficiency Estimation:A Semiparametric Stochastic Cost Frontier Approach and Shanxi Road Passenger Transport Enterprises

传统参数方法在模型设定上过于严格,不贴近现实,忽视了政策等环境变量对我国道路运输企业成本效率的柔性影响,造成估计的偏差。本文结合参数与非参数方法,将传统的柯布道格拉斯随机成本前沿函数模型拓展为一个柔性的、半参数随机成本前沿面板数据模型,应用到考察道路运输企业成本效率这一关键指标研究中。该模型充分考虑到企业异质性和时间等变量对成本边界造成的非中性移动,其技术参数都设定为企业异质效应和时间效应的光滑函数,无效率项被分解为企业特质和时间特质两部分,生产率变化被分解为无效率变化,技术变革和规模变化三部分。通过对山西省公路客运企业成本效率的实证分析发现半参数模型较参数模型估计结果良好。无效率变化指数随时间普遍降低,表明在研究期间效率普遍提高。输入价格的变化,在样本期间下降的趋势大于增加的趋势,技术变革的速度随时间变化非常大,在道路客运环境不成熟完善的环境中,山西道路运输行业经历了快速的技术进步（成本降低）。学习效应导致的技术无效率以及技术进步,有助于生产率的增长（成本降低）,而这些促进是以柔性的方式展现的,并随时间变化。

Traditional parametric method is too strict in the model specification, and it is not realistic since it ignores the flexibility effect of the policy and other environmental variables on the cost efficiency of China＇s road transport enterprises, which creates the assumed deviation. This paper combines parametric methods and non-parametric methods, expanding the traditional Cobb Douglas stochastic cost frontier function model to a flexible, semiparametric stochastic cost frontier panel data model, and apply them to the study of road transportation enterprises＇ cost efficiency. This model also takes full account of the non-neutral movement of boundary cost which caused by heterogeneity of enterprises, time and other variables. Its technical parameters are set for the smooth function of enterprise heterogeneity effect and the time effect. The inefficiency item is decomposed into business characteristics and time characteristics, and the productivity change is decomposed into three parts： invalid rate change, technological change and scale change. The empirical analysis of the cost efficiency of Shanxi highway passenger transport enterprises found that the results of semiparametric model are more satisfying. They show that the inefficiency change index decreased with time, which indicated that the efficiency was generally improved during the research. The downward trend of input prices is greater than the upward trend during the sample period, and at the same time, bigger shifts in technology have happened in less time. In the immature and imperfect atmosphere, Shanxi road transport industry has experienced rapid technological progress with lower cost. Technical inefficiency and technical progress resulting from learning effects contribute to increased productivity with lower cost changing over time, which is shown in a flexible manner.