A BLP Demand Model of Product-Level Market Shares with Complementarity

Ao Wang
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引用次数: 10

Abstract

Applied researchers most often estimate the demand for differentiated products assuming that at most one item can be purchased. Yet simultaneous multiple purchases are pervasive. Ignoring the interdependence among multiple purchases can lead to erroneous counterfactuals, in particular, because complementarities are ruled out. I consider the identification and estimation of a random coefficient discrete choice model of bundles, namely sets of products, when only product-level market shares are available. This last feature arises when only aggregate purchases of products, as opposed to individual purchases of bundles, are available, a very common phenomenon in practice. Following the classical approach with aggregate data, I consider a two-step method. First, using a novel inversion result in which demand can exhibit Hicksian complementarity, I recover the mean utilities of products from product-level market shares. Second, to infer the structural parameters from the mean utilities while dealing with price endogeneity, I use instrumental variables. I propose a practically useful GMM estimator whose implementation is straightforward, essentially as a standard BLP estimator. Finally, I estimate the demand for Ready-To-Eat (RTE) cereals and milk in the US. The demand estimates suggest that RTE cereals and milk are overall complementary and the synergy in consumption crucially depends on their characteristics. Ignoring such complementarities results in misleading counterfactuals.
具有互补性的产品级市场份额BLP需求模型
应用研究人员通常估计差异化产品的需求,假设最多只能购买一种产品。然而,同时多次购买的现象很普遍。忽略多次购买之间的相互依赖可能会导致错误的反事实,特别是因为互补性被排除在外。我考虑了当只有产品级市场份额时,束即产品集的随机系数离散选择模型的识别和估计。最后一个特性出现在只有整体购买产品的情况下,而不是单独购买捆绑产品的情况下,这在实践中是一种非常普遍的现象。在使用聚合数据的经典方法之后,我考虑采用两步方法。首先,利用一种新的反转结果,其中需求可以表现出希克斯互补,我从产品层面的市场份额中恢复了产品的平均效用。其次,在处理价格内生性的同时,为了从平均效用中推断出结构参数,我使用了工具变量。我提出了一个实际有用的GMM估计器,它的实现很简单,本质上是一个标准的BLP估计器。最后,我估计了美国对即食谷物和牛奶的需求。需求估计表明,即食谷物和牛奶总体上是互补的,消费的协同作用在很大程度上取决于它们的特性。忽视这种互补性会导致误导性的反事实。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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