本文欲研究水平產品差異對於下游部分勾結之廠商的影響，假定上游廠商生產同質中間財，下游廠商生產異質最終財，且上、下游廠商各自在其市場進行數量競爭。下游 Cartel 廠商為 Stackelberg 領導者，邊緣廠商為跟隨者，我們分析在不同產品異質程度下，垂直結合廠商的存在是否會促進形成暗默勾結的可能性。研究結果顯示，當產品為完全同質時，僅有與邊緣廠商垂直結合會增加暗默勾結的可行性，與 Cartel 廠商垂直結合反而會阻礙 Cartel 的形成，這是因為與 Cartel 廠商垂直結合的下游廠商背離利潤大於垂直結合前的背離利潤。但當產品趨於異質時，由於與 Cartel 廠商垂直結合的下游背離利潤減少，故當產品差異程度越大，無論是何種垂直結合皆會促進暗默勾結。至於垂直結合對社會福利的影響，就大部分情況而言，垂直結合會發生社會福利改善，惟當臨界折現因子介於極小區間時，因為垂直結合有促進暗默勾結的效果，可能會使社會福利受到損害。

This paper analyzes the impacts of horizontal product differentiation on downstream incomplete collusion. We assume that the upstream firms and the downstream firms compete by choosing quantities in their markets. The downstream cartel firms behave as a Stackelberg leader, and then the fringe firms maximize their profit by choosing the output subsequently. We find that vertical merger with a fringe firm will promote downstream collusion when the downstream firms produce a homogeneous final good. However, vertical merger with a cartel firm will hinder collusion, because vertical merger with a cartel firm obtains profit from deviation larger than no vertical merger. Additionally, vertical merger always promotes downstream collusion when the larger the degree of heterogeneity. This is because the profit from deviation will decrease. About the impacts of vertical merger on social welfare, we find that the existence of vertically-integrated firm would be generally welfare-improving. Only when the critical discount factor is between the smaller range, vertical merger would promote collusion and decrease social welfare.

論文審定書 i
誌謝 ii
摘要 iii
Abstract iv
目錄 v
圖　次 vi
表 次 vii
第一章 前言 1
第二章 文獻回顧 5
第三章 模型 9
第一節 沒有垂直結合 10
第二節 與 Cartel 廠商進行垂直結合 15
第三節 與邊緣廠商進行垂直結合 21
第四章 模型結果分析 25
第一節 部分勾結的靜態穩定條件與動態穩定條件 25
第二節 產品異質性的影響 27
第三節 社會福利分析 37
第五章 結論 44
參考文獻 46
附錄A. 符號 48
附錄B. 動態穩定與靜態穩定 57
附錄C. 產量與利潤 73

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