线上市场价格为何偏离"一价定律"——基于商家平台链接视角的价格离散"跳变"假说

Abstract

Price dispersion is a key indicator of market efficiency, but online markets often display persistent price dispersion despite lower search costs and widespread price-comparison tools. Existing explanations typically treat market structure and consumer search as exogenous, overlooking a key feature of online retailing: Merchants can add or remove product listings across platforms at a low cost, and these listing decisions directly affect pricing. Based on a mixed-strategy pricing model, this paper endogenizes platform-listing choice and examines how consumer composition, search costs, and price discrimination jointly shape pricing and price dispersion. The model includes two competing merchants, two retail platforms, and two types of consumers: loyal consumers and comparison consumers. Merchants may choose single-platform or multi-platform selling. Under uniform pricing, there exists a threshold in consumer composition. Given a platform structure, price dispersion changes gradually; once the threshold is crossed, merchants adjust their platform-listing strategies, which changes pricing strategies and causes discontinuous movements in price dispersion. Entering a rival-occupied platform raises equilibrium prices and expands price dispersion, whereas exiting that platform lowers equilibrium prices and compresses price dispersion. When price discrimination becomes feasible, merchants are more likely to return to single-platform selling, causing another downward jump. The empirical analysis uses daily online product price data. Based on 4.4 million product-day-platform observations, this paper constructs two datasets: an unbalanced product-day panel with about 1.93 million valid observations, and a platform-product-dates dataset with 183945 observations. Price dispersion is mainly measured by the relative price difference, with the coefficient of variation used for robustness checks. Product fixed-effects panel models are employed to examine the effects of platform-count changes, shopping-festival shocks, and weekend conditions on price dispersion and platform listings. The results support the theoretical prediction in three respects. First, in both cross-sectional and time-series analyses, the number of platforms on which a product is sold is significantly positively associated with price dispersion, and more platform access is accompanied by higher average prices. Second, during major shopping festivals such as "6·18" and "Double 11", lower search costs and stronger comparison shopping induce merchants to increase cross-platform listings, which raises price dispersion. Third, weekends display a different pattern: Although search costs may decline, merchants are more able to engage in price discrimination, and therefore reduce platform listings and exhibit lower price dispersion. This paper contributes by incorporating endogenous platform-listing choice into the mixed-strategy pricing framework, distinguishing between gradual and jump changes in price dispersion, and providing a unified explanation for shopping-festival high prices and lower weekend price dispersion. The policy implication is that evaluations of online price dispersion should jointly consider merchants ' platform-switching costs, consumer search costs, and price discrimination capability, rather than mechanically treating price dispersion as evidence of market failure or tacit collusion.