©2009 INFORMS Competing Retailers and Inventory: An Empirical Investigation of General Motors ’ Dealerships in Isolated U.S. Markets

We study the following question: How does competition influence the inventory holdings of General Motors’dealerships operating in isolated U.S. markets? We wish to disentangle two mechanisms by which local competition influences a dealer’s inventory: (1) the entry or exit of a competitor can change a retailer’s demand (a sales effect); and (2) the entry or exit of a competitor can change the amount of buffer stock a retailer holds, which influences the probability that a consumer finds a desired product in stock (a service-level effect). Theory is clear on the sales effect—an increase in sales leads to an increase in inventory (albeit a less than proportional increase). However, theoretical models of inventory competition are ambiguous on the expected sign of the service-level effect. Via a Web crawler, we obtained data on inventory and sales for more than 200 dealerships over a six-month period. Using cross-sectional variation, we estimated the effect of the number and type of local competitors on inventory holdings. We used several instrumental variables to control for the endogeneity of market entry decisions. Our results suggest that the service-level effect is strong, nonlinear, and positive. Hence, we observe that dealers carry more inventory (controlling for sales) when they face additional competition. Key words: inventory competition; empirical; entry; supply chain management; automobile industr