Simon P. Anderson

We model a platform controlling the variety and prices of the products it hosts via a percentage fee on sellers and choosing whether to sell its own products (hybrid mode). We derive a mixed market demand system for differentiated products with monopolistically competitive sellers and a sizeable platform product range. The hybrid platform steers consumers toward its products by charging higher seller fees than pure marketplace. This “insidious steering” intensifies the larger the platform's product footprint. Hybrid mode harms consumers compared to pure marketplace unless fringe entry is sufficiently inelastic.

We compile an IO toolkit for aggregative games with positive and normative comparative statics results for asymmetric oligopoly in the short and long run. We characterize the class of aggregative Bertrand and Cournot oligopoly games, and the subset for which the aggregate is a summary statistic for consumer welfare. We close the model with a monopolistically competitive fringe for long‐run analysis. Remarkably, we show strong neutrality properties in the long run across a wide range of market structures. The results elucidate aggregative games as a unifying principle in the literature on merger analysis, privatization, Stackelberg leadership, and cost shocks.

We show for CES demands with heterogeneous productivities that profit, revenue and output distributions lie in the same closed power family as the productivity distribution (e.g., the ‘Pareto circle’). The price distribution lies in the inverse power family. Equilibrium distribution shapes are linked by linear relations between their density elasticities. Introducing product quality decouples the CES circle, and reconciles Pareto price and Pareto sales revenue distributions. We use discrete choice underpinnings to find variable mark-ups for a more flexible demand formulation bridging CES to logit and beyond. For logit demand, exponential (resp. normal) quality-cost distributions generate Pareto (log-normal) economic size distributions.

Consumer “multihoming” (watching two TV channels, or buying two news magazines) has surprisingly important effects on market equilibrium and performance in (two‐sided) media markets. We show this by introducing consumer multihoming and advertising finance into the classic circle model of product differentiation. When consumers multihome (attend more than one platform), media platforms can charge only incremental value prices to advertisers. Entry or merger leaves consumer prices unchanged under consumer multihoming, but leaves advertiser prices unchanged under single‐homing: Multihoming flips the side of the market on which platforms compete. In contrast to standard circle results, equilibrium product variety can be insufficient under multihoming.

The more functionalities a good offers, the greater is its perceived quality. Equilibrium prices in standard spatial competition models depend solely on quality differences. We assume that new functionalities are more appreciated the closer a product is to a consumer's ideal variety. Prices are then increasing in functionality levels. Furthermore, we endogenize whether consumers buy only one of two varieties (single‐purchase) or both (multipurchase). Under multipurchase, there might be a hump‐shaped relationship between equilibrium prices and functionality levels. Therefore, it could be optimal for each supplier to sacrifice sales and set prices so high that multipurchase is eliminated.

We derive equilibrium incentives to use comparative advertising that pushes up own brand perception and pulls down the brand image of targeted rivals. Data on content and spending for all TV advertisements in Over‐The‐ Counter (OTC) analgesics enable us to construct matrices of rival targeting expenditures and estimate the structural model. Using brands' optimal choices, these attack matrices identify diversion ratios, from which we derive comparative advertising damage measures. We find that comparative advertising causes more damage to the targeted rival than benefit to the advertiser. We simulate banning comparative advertising to find industry profits rise.