本文分析具有市場力的製造商如何影響零售商的垂直差異產品線，其中，高品質產品由獨占廠商生產，低品質產品由競爭市場提供，兩家零售商可選擇僅銷售高品質產品、僅銷售低品質產品或銷售兩種產品。本文發現，當獨占製造商偏好與一家零售商簽約時，簽約的零售商會銷售兩種產品，另一家零售商僅銷售低品質產品。但在固定低品質的條件下，隨著生產高品質產品的成本上升，批發價上升。當成本升高至臨界值，為了避免兩家零售商都不銷售高品質產品的情況，製造商會選擇降低批發價，提出一份讓兩家零售商都會簽訂的合約。此時，兩家零售商會同時銷售高、低品質兩種產品。

This research investigates how manufacturer’s market power determines vertically differential product line in retailing. The high-quality good is produced by a monopolist, and the low-quality good is made by a competitive fringe. The product line chosen by retailers in equilibrium are either selling high-quality goods only, low-quality goods only, or selling both goods. We demonstrate that the monopolist prefers to make a contract with one retailer, and the retailer sell both high-quality goods and low-quality goods to consumers, while the other retailer only sell low-quality goods. As the cost of production of high-quality goods rises, wholesale price increases under the condition of fixed low-quality. To avoid the situation that there is no high-quality goods sold in the market, the monopolist will reduce wholesale price and make contracts with two retailers simultaneously when the cost of production reaches critical values. Therefore, two retailers sell both high-quality and low-quality goods to consumers.

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