Tianle Song

We study a homogeneous-goods market with two identical incumbent suppliers, a potential entrant, and multiple downstream retailers. A market price is supra-competitive if it exceeds the incumbents' competitive equilibrium price in the absence of entry. We show that supra-competitive market prices arise only in exclusionary equilibria, in which the incumbents use transfers to retailers to prevent accommodation of entry. Exclusion can occur even when the entrant is highly efficient or transfers are small. These qualitative results extend to an asymmetric-information setting in which the entrant's unit cost is privately known.

In user-generated content platforms, influencers sort into multiple tiers, with bottom-up one-way attention flows. This paper develops a model where having more followers increases the marginal benefit of providing content. Every strict Nash equilibrium exhibits a nested upward-linking structure: players sort endogenously into tiers, with higher-tier players providing more content, attracting more followers, and following fewer others. The proportion of influencers is bounded below by a strictly positive number that does not depend on population size, in contrast with the law of the few in public goods networks where contributors vanish as the population grows. All equilibria are inefficient. Efficiency requires more tiers of influencers, not fewer. The key to understanding these patterns is influence-content complementarity, which generates endogenous hierarchy with bottom-up attention flows from identical players.

We study monopoly pricing under limited demand information with a competitive-ratio objective, defined as the minimum ratio of realized profit to ex post optimal profit across all admissible demand curves. We characterize the unique price that maximizes the competitive ratio and identify representative inverse demand curves that attain this ratio. Moreover, we argue that the competitive-ratio criterion can be more attractive than the worst-case-profit criterion from a realized-profit perspective. The model also provides a tractable framework for analyzing pricing with arbitrary patterns of observed demand data and with an uncertain choke price.

This paper examines the formation of influencer networks in user-generated content markets. Players decide whether to produce content, its quality, and whom to follow. Each strict equilibrium network is a nested upward-linking network where different levels of influencers can co-exist, with those at higher tiers providing higher-quality content and being followed by players in all lower tiers. Under a wide range of parameters, all payoff-dominant strict equilibria conform to the law of the vital few: a small yet significant proportion of players produce all the content. However, unlike previous models where the number of influencers is limited and their proportion diminishes rapidly to zero, the complementarity between influence and content provision causes the number of influencers to grow indefinitely with the population. For sufficiently large populations, a single nested upward-linking network connecting all players can emerge, even when players have heterogeneous preferences over content categories.

This paper studies the effects of social status—a socially recognized ranking of individuals—on prosocial behavior. We use a laboratory experiment and propose a theory to address this issue. In a one-shot game, two players, whose social status is either earned or randomly assigned, jointly make effort contributions to a project. Player 1 first suggests an effort level for each player to player 2 who then determines the actual effort levels. Deviation from the proposal is costly. We find causal evidence that high-status players are less selfish than their low-status counterparts. In particular, high-status players 2 provide relatively more effort, ceteris paribus, than those with low status. The experimental results and theoretical framework suggest that a high social ranking yields more social behavior and that this can be attributed to the sense of responsibility that it gives.