本文目的為分別探討當產品品質創新無網絡效益與有顯著網絡效益之下，廠商與社會最適品質、網絡大小與定價如何決定，進一步分析兩種狀況下，網路外部性對市場之影響有何不同，以了解品質創新之網絡效益會如何影響產品品質與網絡大小。主要結果為，若網絡效果僅受網絡大小影響，即產品品質創新無網絡效益，隨著網路外部性增加，獨佔廠商的產品品質與價格會下降。然而，當考慮產品品質創新具有網絡效益，隨著網路外部性增加，獨佔廠商的產品品質、價格則會上升。此外，在上述兩種情況下，我們都發現獨佔廠商的產品品質會低於社會最適。隨著網路外部性增加，在產品品質創新無網絡效益下，獨佔廠商與社會最適的產品品質差距會擴大，社會福利的差距會縮小；在產品品質創新具網絡效益下，獨佔廠商與社會最適的產品品質與社會福利差距皆會擴大。我們亦發現，在獨佔及社會最適之下，若品質創新具有顯著網絡效益時，相較於無網絡效益，會進一步提高產品品質及價格，然而總產量(網絡大小)則會下降。

This paper examines the effects of network externalities on the product quality, network size, and product price of a monopolist under two different cases where the network benefits of quality are insignificant and significant, respectively. Our results show that, if the network benefits of quality are insignificant, a higher extent of network externalities decreases both the product quality and price. However, if the network benefits of quality are insignificant, a higher extent of network externalities increases both the product quality and price. In addition, compared with the social optimum, the monopolist’s product quality is insufficient in both the two cases. However, if the network benefits of quality innovation are insignificant, an increase in the extent of network externalities enlarges the quality gap between the monopoly and the social optimum, but it may narrow the welfare gap between them. However, if the network benefits of quality innovation are significant, an increase in the extent of network externalities enlarges both the quality and welfare gaps between the monopoly and the social optimum. Furthermore, we find that, compared with the case with insignificant network benefits from quality innovation, product quality is higher but the output (i.e., network size) is lower under significant network benefits from quality innovation.

審定書 i
摘要 ii
Abstract iii
目錄 iv
圖目錄 v
第一章 前言 1
第二章 文獻回顧 3
第三章 產品品質不具網絡效益 6
3.1 獨佔市場分析 6
3.2 社會最適分析 8
第四章 產品品質創新具顯著網絡效益 11
4.1 獨佔市場分析 11
4.2 社會最適分析 14
第五章 最優社會最適品質之分析 17
第六章 結論 19
參考文獻 25
附錄A 27
附錄B 28

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