作者：张勋 王旭 万广华 孙芳城
关键词：基础设施 企业库存 市场扩张 运输成本 新结构经济学
A Unified Framework of Road Infrastructure’s Growth Effect
ZHANG Xun, WANG Xu, WAN Guanghua and SUN Fangcheng
Summary：We studied the effect of road infrastructure on economic growth through its effect on a firm’s inventory. Different from previous studies,we aim to build up a unified framework to analyze the growth effect of road infrastructure.
In this paper,we propose three hypotheses to test the underlying mechanisms through which road infrastructure affects inventory and thus contributes to economic growth. First, road infrastructure helps firms to expand their market, promotes output and sales, and increases demand for inventory. Second, road infrastructure brings about competition in the domestic market, which reduces the market expansion effect and the inventory demand. Third, road infrastructure reduces transportation cost, which on the one hand increases efficiency and on the other hand helps save inventory storage.
Empirically,we used data from the Annual Survey of Industrial Firms (ASIF) combined with road information. To analyze the transmission channels underlying the relationship of the road infrastructure and inventory,we used the mediation model and analyzed the effect of a change in the coefficient of the road infrastructure on the inventory upon the addition of the mediating variables. As the dependent variable,we used nonfinished goods as the inventory. For the road infrastructure variable, different from previous studies, we measured a firm’s accessible road infrastructure using the road area of both local and neighboring cities. The mediating variables included market size, competition, and transportation cost. For market size, we directly used the log of sales as a proxy. For competition, we used the cityindustryyear Herfindahl index. For transportation cost, we used the log of the input lead time. Input lead time was measured as 365/(cost of goods sold/accounts payable), which approximated the number of days it took for firms to source their inputs.
The baseline empirical results show that road infrastructure helps to reduce inventory. We used the mediating model to verify the underlying transmission channels. We found that once the market size variable was added to the baseline regression, the coefficient for road infrastructure was further reduced. Moreover, upon the regression of market size on the infrastructure, we found a positive relationship. These two findings suggest that the road infrastructure helped to increase the market size and thus increased the inventory demand. Similarly, once the competition and transportation cost variables were added, the coefficient for road infrastructure increased. Moreover, we found that road infrastructure led to competition and transportation cost reduction. These findings indicate that the channels of competition and transportation cost reduction induced by road infrastructure reduced inventory demand. The results confirm the three transmission channels through which road infrastructure affected inventory and economic growth.
We further verified the channels through which road infrastructure affected inventory and economic growth by conducting heterogeneous analysis and dividing the samples according to the different properties of the firms. We divided the samples by product heterogeneity to verify the market expansion channel, by entry barrier to verify the competition channel, and by weight per value of product to verify the transportation cost channel. We found that firms with higher heterogeneity, lower entry barriers, and more weight per value of product were more significant in the market expansion, competition, and transportation cost channels.
Finally, we conducted a robustness check by considering measurement error of the road infrastructure and definition of the entry barrier, incorporating the effect of the communication infrastructure and industrial dynamics, and the instrumental variable of road infrastructure by using the number of post houses in the Ming Dynasty. The results remained robust.
This paper enhances the literature by providing a unified framework for the relationship between road infrastructure and inventory and for estimating the causal effect on economic growth.
Keywords： Road Infrastructure; Inventory; Market Expansion; Transportation Cost; New Structural Economics
JEL Classification： E22, H54, R4
姓名：张勋 王旭 万广华 孙芳城 工作单位：