Dynamic Demand Estimation in Auction Markets

Economists have developed empirically tractable demand systems for fixed price markets. In contrast, empirical auction techniques treat each auction in isolation, ignoring market interactions. We provide a framework for estimating demand in a large auction market with a dynamic population of buyers with unit demand and heterogeneous preferences over a finite set of differentiated products. We offer an empirically tractable equilibrium concept under which bidders behave as though they are in a steady-state, characterize bidding, and prove existence of equilibrium. Having developed a demand system, we show that it is non-parametrically identified from panel data, and that this result is robust to typical data limitations, reserve prices, random coefficient demand, public signals that refine beliefs about market conditions, unobserved heterogeneity, idiosyncratic preferences, and random latent outside options. We apply the model to estimate demand and measure consumer surplus in the market for compact cameras on eBay. Our analysis highlights the importance of both dynamic bidding strategies and panel data sample selection issues when analyzing these markets.