本文研究了雙渠道分別在兩種產品差異化模型中的影響。首先，利用垂直產品差異化模型來探討只有一家實體商店和雙渠道間的差異。我們發現要素價格和實體店價格在雙渠道都比較低。如果網路店能夠允許存在，零售商將選擇雙渠道，而雙渠道對製造商來說不一定有利。此外，消費者剩餘在雙渠道時比較高，但社會福利不明確。第二，考慮水平產品差異化模型。我們發現雙通道導致更高的要素價格和實體店價格。雙渠道對零售商和製造商都有利，但是雙渠道導致消費者剩餘降低，社會福利提高。

This paper studies the effect of dual channels in two types of product differentiation models. First, a vertical product differentiation model is utilized to examine the differences between physical (off-line) store only and dual channels with both on-line and off-line stores. It is found that both input and physical prices are lower in dual channels than those in the physical store only, the retailer will choose dual channels when the on-line store is available, and the manufacturer may not prefer dual channels run by the retailer. Furthermore, the consumer surplus is higher in dual channels than that in physical store only, however, the effect on social welfare is ambiguous. Second, a horizontal product differentiation model is considered. It is found that dual channels lead to higher input and physical prices. When the on-line store exists in the market, the retailer chooses dual channels which also benefit the manufacturer. Comparing to the physical store only, dual channels lead to lower consumer surplus and higher social welfare.

Chapter 1. Introduction. 1
1.1 Research motivation. 1
1.2 Related literatures. 2
1.3 Research framework. 4
Chapter 2.Vertical product differentiation model. 5
2.1 Basic model. 5
2.2 The equilibria of physical store only. 7
2.3 The equilibria of dual channels. 8
2.4 The effect of dual channels. 10
2.5 Welfare analysis. 12
2.6 Brief summary. 13
Chapter 3. Horizontal product differentiation model. 13
3.1 Basic model. 13
3.2 The equilibria of physical store only. 15
3.3 The equilibria of dual channels. 16
3.4 The effect of dual channels. 18
3.5 Welfare analysis. 19
3.6 Brief summary. 20
Chapter 4. Conclusion. 20
Appendix. 22
References. 26

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