Abstract: With much change of the market and the diversification of demand, variety and small batch production mode has increasingly become a main way of manufacturing. In this context, driven by the pressure to control operating costs and focus on core competencies, group purchasing has been drawing heightened attention from practitioners and researchers in the last decade. Although, in the big data age, information sharing is an important part and essential support of group purchasing, a major challenge is the reluctance of some firms to share information because of the fear of loss. To address this incentive problem, a group purchasing supply chain consisting of one group purchasing organization (GPO) and two competing manufacturers is studied. The manufacturers purchase a common component from the GPO and compete in quantity by selling partially substitutable products in a common market. Each manufacturer is endowed with some private and imperfect information about the uncertain demand intercept and is allowed to share partial information with the GPO. A three-stage game model is used to study the participants' equilibrium decisions. In the first stage, each manufacturer decides a level of information to share with the GPO before observing the demand, and subsequently, shares the observed demand information with the GPO according to the specified level. In the second stage, the GPO sets a unified wholesale price of the component for the manufacturers. In the third stage, upon learning the wholesale price, each manufacturer decides his order quantity.Our research mainly contains the following four parts. Firstly, by solving the model, the impacts of competition intensity and information accuracy on the equilibrium decisions are analyzed. Secondly, we explore the value of information sharing and reveal the feasible condition of information sharing. Thirdly, a two-part compensation contract is proposed as an incentive strategy for information sharing. Finally, the coordinating effect of information sharing is shown by comparing with the performance under centralized decision setting, companied with numerical examples. The results indicate that both manufacturers have no incentive to share their private information with the GPO in equilibrium. However, information sharing can coordinate the competition between the manufacturers. When the competitive intensity exceeds a certain threshold, the supply chain system can be benefited from information sharing. Only then the manufacturers can be incented to share complete information by a two-part compensation contract. Based on this incentive contract, the supply chain system can realize higher expected profit under decentralized decision setting than that under centralized decision setting when both the competition intensity and demand variation are large enough.In summary, in this paper, group purchasing is studied with an informational perspective and a new insight is provided into the coordinating effect of vertical information sharing on horizontal competition. The findings in this paper can provide academic and practical inspirations on group purchasing.

Key words: information sharing, demand forecast, group purchasing, quantity competition, incentives