本文建構一個具有網路效果與垂直產品差異化的雙佔模型，探討網路外部性的強弱對於高低兩品質廠商的生產品質水準以及價格的影響。兩廠商在第一階段選擇產品品質，第二階段則分別考慮進行價格或數量競爭兩種狀況。研究結果指出，當網路外部性增加時，在價格競爭下，低品質廠商會降低其生產品質，高品質廠商生產品質則會先降後升，高品質廠商價格會先下降後上升，低品質廠商價格會下降，高品質廠商需求量會增加，低品質廠商需求量會先增加後減少；然而，在數量競爭下，低品質廠商會提升其生產品質，高品質廠商生產品質則會降低，高品質廠商價格會下降，低品質廠商價格會先降後升，此外，兩家廠商需求量則皆會增加。

This paper builds a duopoly model with network externality and vertical product differentiation to examine the effects of network externality on the product quality, network size and the profits of high- and low-quality firms under different types of competition. The results indicate that, under price competition, when network externality increases, the low-quality firm lowers its product quality while the high-quality firm first decreases and then increases its product quality. By contrast, under quantity competition, the low-quality firm lowers its product quality while the high-quality firm increases its product quality.

審定書 i
摘要 ii
Abstract iii
目錄 iv
圖表目錄 vi
第一章 前言 1
第二章 文獻回顧 4
第三章 模型設定 7
3.1價格競爭 8
【命題一】 10
【命題二】 12
3.2數量競爭 13
【命題三】 15
【命題四】 16
第四章：結論 18
中文參考文獻 21
英文參考文獻 22
附錄A 23
證明【命題一】： 23
附錄B 24
證明【命題二】： 24
附錄C 25
證明【命題三】： 25
附錄D 26
證明【命題四】： 26

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李娓瑋、黃健杰、蔡淑琴，2007，垂直產品差異、網絡效果之品質與價格競爭分析，經濟與管理論叢，Vol.3, No. 1,頁49-65。
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