关键词: 数字经济, 双边平台, 价格歧视, 多归属, Hotelling模型, 子博弈精炼纳什均衡

Abstract: The digital economy has become an increasingly pivotal sector in the growth trajectory of China’s overall economy. Digital platforms serve as the principal arenas for transactions within this digital economy, effectively acting as its backbone. While the implementation of stringent antitrust regulations has increasingly limited the capacity of these platforms to openly enforce exclusivity contracts, digital platforms still retain the ability to subtly influence users through the traditional economic tactic of discriminatory pricing. This approach is more covert. This paper aims to investigate the impact of price discrimination by digital platforms, particularly targeting sellers based on their affiliations, as a more covert means of influencing user behavior.
This paper develops a competitive model for duopolistic digital platforms where both sellers and buyers exhibit heterogeneous preferences. We explore the impact on social welfare and platform pricing strategies when sellers and buyers can opt for multi-homing—that is, joining multiple platforms. Specifically, the model investigates the effects of third-degree price discrimination by the platforms based on whether sellers choose to multi-home or not. To capture the preferences of sellers and buyers, we employ the Hotelling model and position the duopolistic platforms at the two trisection points on the Hotelling line. This approach allows us to mitigate the interference caused by varying preferences when investigating the impact of price discrimination.
The findings indicate that third-degree price discrimination leads to an increase in seller surplus while simultaneously reducing buyer surplus and overall social welfare. The primary reason for this outcome is that price discrimination intensifies competition between the duopolistic platforms for sellers, thereby driving down the prices set for them.From the perspective of sellers, the duopolistic platforms find themselves in a Prisoner’s Dilemma, intensifying competitive pressures. These escalated competitive forces subsequently cascade to the buyers, ultimately burdening buyers who are not subject to price discrimination. Specifically, the platforms raise Prices targeted at these buyers, resulting in a reduction in buyer surplus. The third-degree price discrimination also alters the platforms’pricing strategies for both sellers and buyers, giving rise to skewed pricing phenomena: both platforms lower prices for sellers and raise prices for buyers, while simultaneously reducing the number of sellers and buyers that join both platforms.An increase in the number of sellers (or buyers) joining a platform leads to enhanced positive externalities for buyers (or sellers), thereby improving overall social welfare. However, the price reductions induced by platform price discrimination fail to increase the number of sellers joining the platforms. Instead, they elevate the costs of multi-homing for sellers, leading to a reduction in their numbers and a consequent detrimental impact on social welfare. These conclusions hold stable under the conditions of asymmetry between sellers and buyers, as well as varying levels of service heterogeneity provided by the platforms.
In future research, we will examine the impact of third-degree price discrimination by platforms based on whether sellers are multi-homing, specifically focusing on its impact on platform profitability. We intend to analyze this impact using methods that do not rely on explicit solutions. Furthermore, we aim to distill economically meaningful and more concise conditions to ensure the existence and uniqueness of symmetric equilibria. Additionally, we will explore the effects of price discrimination on user surplus and social welfare under alternative distributions of user preferences.

Key words: digital economy, two-sided platform, price discrimination, multi-homing, Hotelling model, subgame perfect Nash equilibrium