本文以Hotelling Model來描述系統產品間水平差異問題，設立系統產品的兩互補性零件皆為價格競爭之雙占模型，討論在不同的整合結構下，市場競爭狀態的分佈情形、系統產品價格之比較與福利分析。本文發現在產品水平差異性小時，平行垂直整合廠商之系統產品價格較獨立廠商時為高，此結果與一般垂直整合下系統產品價格的變化有所不同。在本文中平行垂直整合結構除了內化互補品的垂直外部性外，也內化了系統產品間的水平替代性，使得平行垂直整合後系統產品價格不降反升。而在福利分析方面，直接競爭與市場相接之市場競爭狀態下，不論整合結構為何，其社會福利皆滿足社會最適。然而在區域性獨占時，組合商品競爭與完全整合兩種整合型態最接近社會福利極大，其次是平行垂直整合，社會福利最小的是獨立廠商與平行水平整合兩種情況。

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