标题： 距离在世界贸易网络中的作用 显示英文标题

标题： The role of distances in the World Trade Web

摘要： 在经济文献中，地理距离被视为任何旨在量化国家间贸易的理论模型中必须包含的基本因素。 定量上，距离进入所谓的引力模型，这些模型成功预测了非零贸易流量的权重。 然而，最近的研究表明，引力模型无法再现世界贸易网络的二元拓扑结构。 在本文中，提出了一种不同的方法：使用指数随机图的形式主义，并将距离作为约束条件，施加于先前选定的图集合上。 然后，利用编码在地理距离中的信息，通过在度度相关性和互惠结构上进行测试，来解释世界贸易网络的二元结构。 这导致定义了一个结合空间和非空间效应的新零模型。 通过Akaike信息准则和贝叶斯信息准则，比较了空间约束与非空间约束的有效性。 尽管人们普遍认为世界贸易网络强烈依赖于距离，但我们的分析结果表明，距离在塑造世界贸易网络的二元结构中并不起关键作用，而编码在互惠性中的信息在解释观察到的模式方面要有用得多。 显示英文摘要

摘要： In the economic literature, geographic distances are considered fundamental factors to be included in any theoretical model whose aim is the quantification of the trade between countries. Quantitatively, distances enter into the so-called gravity models that successfully predict the weight of non-zero trade flows. However, it has been recently shown that gravity models fail to reproduce the binary topology of the World Trade Web. In this paper a different approach is presented: the formalism of exponential random graphs is used and the distances are treated as constraints, to be imposed on a previously chosen ensemble of graphs. Then, the information encoded in the geographical distances is used to explain the binary structure of the World Trade Web, by testing it on the degree-degree correlations and the reciprocity structure. This leads to the definition of a novel null model that combines spatial and non-spatial effects. The effectiveness of spatial constraints is compared to that of nonspatial ones by means of the Akaike Information Criterion and the Bayesian Information Criterion. Even if it is commonly believed that the World Trade Web is strongly dependent on the distances, what emerges from our analysis is that distances do not play a crucial role in shaping the World Trade Web binary structure and that the information encoded into the reciprocity is far more useful in explaining the observed patterns.