A Balls-and-Bins Model of Trade
提出一个球与箱统计模型，将贸易货物分配到国家、产品和企业的过程形式化为球落入箱中，该模型能再现零贸易流和多元产品、多元目的地出口商的频率，但高估了出口企业的比例。
Many of the facts about the extensive margin of trade—which firms export, and how many products are sent to how many destinations— are consistent with a surprisingly large class of trade models because of the sparse nature of trade data. We propose a statistical model to account for sparsity, formalizing the assignment of trade shipments to country, product, and firm categories as balls falling into bins. The balls-and-bins model quantitatively reproduces the pattern of zero product- and firm-level trade flows across export destinations, and the frequency of multiproduct, multidestination exporters. In contrast, balls-and-bins overpredicts the fraction of exporting firms.