中文摘要
本文考察墨西哥农村地区基本生活必需品的价格。我们记录发现，以数量折扣形式出现的非线性定价普遍存在，基本生活必需品的数量折扣幅度相当可观，而且广为人知的有条件现金转移支付项目Progresa显著提高了数量折扣，尽管既有研究表明，该项目平均而言并未影响单位价格。为解释这些现象，我们提出了一个价格歧视模型，将Maskin和Riley（1984）以及Jullien（2000）的模型包含为特例。在该模型中，消费者的偏好存在差异，并且由于基本生存约束，其购买商品的支付能力也存在差异。我们表明，在温和条件下，消费者面临异质性基本生存约束或预算约束的模型，等价于消费者拥有异质性外部选择的模型。我们利用已有结论刻画均衡价格表，该价格表是数量的非线性函数。我们分析非线性定价对市场参与的影响，以及当消费者面临不同约束时，类似于Progresa、覆盖整个市场的转移支付所产生的影响。我们表明，在常见假设下，仅凭单一市场的价格和数量数据即可对该模型进行结构识别。我们使用墨西哥市镇和聚居地中三种常见消费商品的数据估计该模型。有趣的是，我们发现，相对于线性定价，非线性定价使大量家庭受益，包括消费量较小的家庭，这主要是因为非线性定价引致了更高的市场参与程度。我们还表明，Progresa转移支付影响了所研究的三种商品的价格表斜率，使价格表变得更为陡峭，这与我们的模型一致，并导致价格歧视强度增加。最后，我们发现，该模型的一个简化形式能够解释该项目引起的价格表变动；在这一简化形式中，数量折扣的幅度取决于村庄内购买数量分布的风险率。
Abstract
This paper examines the prices of basic staples in rural Mexico. We document that nonlinear pricing in the form of quantity discounts is common, that quantity discounts are sizable for basic staples, and that the well‐known conditional cash transfer program Progresa has significantly increased quantity discounts, although the program, as documented in previous studies, has not affected unit prices on average. To account for these patterns, we propose a model of price discrimination that nests those of Maskin and Riley (1984) and Jullien (2000), in which consumers differ in their tastes and, because of subsistence constraints, in their ability to pay for a good. We show that under mild conditions, a model in which consumers face heterogeneous subsistence or budget constraints is equivalent to one in which consumers have access to heterogeneous outside options. We rely on known results to characterize the equilibrium price schedule, which is nonlinear in quantity. We analyze the effect of nonlinear pricing on market participation as well as the impact of a market‐wide transfer, analogous to the Progresa one, when consumers are differentially constrained. We show that the model is structurally identified from data on prices and quantities from a single market under common assumptions. We estimate the model using data on three commonly consumed commodities from municipalities and localities in Mexico. Interestingly, we find that relative to linear pricing, nonlinear pricing is beneficial to a large number of households, including those consuming small quantities, mostly because of the higher degree of market participation that nonlinear pricing induces. We also show that the Progresa transfer has affected the slopes of the price schedules of the three commodities we study, which have become steeper as consistent with our model, leading to an increase in the intensity of price discrimination. Finally, we find that a reduced form of our model, in which the size of quantity discounts depends on the hazard rate of the distribution of quantities purchased in a village, accounts for the shift in price schedules induced by the program.