Zi Yang Kang

Zi Yang Kang
PhD Student, Economic Analysis & Policy
PhD Program Office Graduate School of Business Stanford University 655 Knight Way Stanford, CA 94305

Zi Yang Kang

Working Papers

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(with Shosh Vasserman) Economists routinely make functional form assumptions about consumer demand to obtain welfare estimates—often for convenience, tractability, or both. How sensitive are welfare estimates to these assumptions? In this paper, we answer this question by providing bounds on welfare that hold for families of demand curves commonly considered in different literatures. We show that typical functional forms—such as linear, exponential and CES demand—are extremal in different families: they yield either the highest or lowest welfare estimate among all demand curves in those families. To illustrate the flexibility of our approach, we apply our results to the welfare analysis of trade tariffs, income taxation, and surge pricing.

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How does a private market influence the optimal design of a public program? In this paper, I study a designer who has preferences over how a public option and a private good are allocated. However, she can design only the public option. Her design affects the distribution of consumers who purchase the private good—and hence equilibrium outcomes. I characterize the optimal mechanism and show how it can be computed explicitly. I derive comparative statics on the value of the public option and show that the optimal mechanism generally rations the public option. Finally, I examine implications on the optimal design when the designer can intervene in the private market or introduce an individual mandate.

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I consider the welfare and profit maximization problems in markets with externalities. I show that when externalities depend generally on allocation, a Pigouvian tax is often suboptimal. Instead, the optimal mechanism has a simple form: a finite menu of rationing options with corresponding prices. I derive sufficient conditions for a single price to be optimal. I show that a monopolist may ration less relative to a social planner when externalities are present, in contrast to the standard intuition that non-competitive pricing is indicative of market power. My characterization of optimal mechanisms uses a new methodological tool—the constrained maximum principle—which leverages the combined mathematical theorems of Bauer (1958) and Szapiel (1975). This tool generalizes the concavification technique of Aumann and Maschler (1995) and Kamenica and Gentzkow (2011), and has broad applications in economics.

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(with Jan Vondrák) This paper studies fixed-price mechanisms in bilateral trade with ex ante symmetric agents. We show that the optimal price is particularly simple: it is exactly equal to the mean of the agents’ distribution. The optimal price guarantees a worst-case performance of at least 1/2 of the first-best gains from trade, regardless of the agents’ distribution. We also show that the worst-case performance improves as the number of agents increases, and is robust to various extensions. Our results offer an explanation for the widespread use of fixed-price mechanisms for size discovery, such as in workup mechanisms and dark pools.