臺灣博碩士論文加值系統

摘要
本篇論文在不完全競爭市場下，由三個不同的角度切入，探討從價稅與從量稅的優劣。
論文的第一部分為，我們在需求或成本不確定下，探討從價和從量稅之優劣。我們的研究發現: 第一，當不確定來自廠商的成本面時，無論是獨占或寡占市場，從量稅皆有可能優於從價稅；當市場趨近於完全競爭時，從量稅在福利上嚴格優於從價稅。第二，當不確定性來自市場的需求面時，在獨占和寡占市場下都得到從價稅優於從量稅；當市場趨近於完全競爭時，從量稅與從價稅等價。此部分的討論我們放在論文的第二章。
論文的第二部分為，同時考慮產品異質和成本異質的情況下，比較從價和從量稅之優劣。我們獲得以下主要結論：第一、給定產業總產量不變下，當品質差大於邊際成本差時，從量稅有可能優於從價稅；第二、除了品質差異與成本差異外，若商品間還存在水平差異，水平差異會加強從量稅的優越性(superiority)，第三、無論廠商間進行Cournot或Bertrand競爭，上述兩項結果都成立。第四、當品質差大於邊際成本差時，從量稅不僅僅在福利上優於(welfare superior)從價稅，同時柏雷圖順序(Pareto Ranking)也可能反轉。此議題的探討我們放在論文的第三章。
由於補貼可以視為負的課稅，因此論文的第三部分我們探討從量補貼、需求從價補貼與成本從價補貼三種補貼政策之相對優劣。我們得到：不論在本國產業政策或出口補貼政策上，需求從價補貼政策是三種補貼政策中最差的政策；從量補貼政策與成本從價補貼政策之間的優劣則取決於規模經濟與規模不經濟。此部分的研究結果我們放在論文的第四章。
在單純的不完全競爭市場下，傳統文獻得到從價稅必定優於從量稅。然而，當考慮了(1) 存在成本不確定性，或(2) 同時存在產品異質和成本差異時，我們得到從量稅皆有可能優於從價稅。這結果與傳統文獻有很大的差異，也為現實中兩種課稅制度同時存在的現象提出一種可能的解釋。其次，在比較三種補貼研究中，我們得到需求從價補貼是三種補貼政策中最差的政策，至於成本從價補貼與從量補貼何者較好，則取決於規模經濟與規模不經濟。這結果為現實世界中從量補貼和成本從價補貼大量存在的現象提供了理論基礎。

Abstract
This dissertation consists of three independent articles in studying the superiority of an ad valorem tax over a specific tax.
First of all, we discuss the superiority between these two tax regimes in the presence of demand and cost uncertainties in chapter 2. We obtain the following main results. First, when cost uncertainty is involved, a specific tax can be superior to an ad valorem tax regardless of whether the market is monopolistic or oligopolistic. When the market is close to perfect competition, a specific tax is welfare superior to an ad valorem tax. Second, when demand uncertainty is considered, an ad valorem tax is welfare superior to a specific tax in monopoly and oligopoly markets. However, both tax regimes become equivalent when the market is approaching perfectly competitive.
Next, by taking into account product differentiation and cost difference, we examine the superiority between these two tax regimes in chapter 3 of the dissertation. The main results are derived as follows. First, given a fixed total output, a specific tax can be superior to an ad valorem tax if the quality difference is larger than the marginal-cost difference. Second, provided that products are differentiated in quality levels, in horizontal levels, and in marginal costs, a rise in the difference in horizontal levels will enhance the superiority of a specific tax over an ad valorem tax. Third, the above two results remain valid, regardless of whether the mode of competition is Cournot or Bertrand. Finally, when the difference in quality levels is larger than the difference in marginal costs, not only is a specific tax welfare superior to an ad valorem tax, but the former also Pareto dominates the latter.
Thirdly, it is well recognized that subsidy can be regard as a negative tax. Accordingly, we analyze the superiority among the specific, demand and cost ad valorem subsidies in an industrial and export policies in chapter 4 of the dissertation. Given the same total output, we show that the demand ad valorem subsidy is the least efficient policy, regardless of whether it is measured in regard to the industrial or export subsidy policy. The superiority between the specific and cost ad valorem subsidies hinges upon economies or diseconomies of scale in the industry.
Generally speaking, if the market is imperfectly competitive, the traditional result is that an ad valorem tax is superior to a specific tax. However, we show in this dissertation that while considering (1) firms with cost uncertainty, or (2) the presence of cost difference and product differentiation, a specific tax can be superior to an ad valorem tax. This result is not only sharply different from the traditional result in literature, but can also be provided as possible explanations for practical examples that a specific tax is also popular in the real world. Furthermore, we show that the demand ad valorem subsidy is the least efficient policy in the above-mentioned three subsidy regimes, while the superiority between the specific and cost ad valorem subsidies hinges upon the economies or diseconomies of scale in the industry. This result provides a theoretical rationale for the phenomenon that the specific and the demand ad valorem subsidies are popular in the real world.

Contents
Chapter 1. Introduction 1
Chapter 2. The Comparison between Ad Valorem and Specific Taxation under Uncertainty 6
2.1. Introduction 6
2.2. The Model 10
2.3. Comparison between specific and ad valorem taxes 12
2.3.1. Cost uncertainty 15
2.3.2. Demand uncertainty 24
2.4. Concluding Remarks 27
Chapter 3. Specific versus Ad Valorem Taxes in the Presence of Cost Difference and Product Differentiation 28
3.1. Introduction 28
3. 2. The Model 32
3.3. Comparison between specific and ad valorem taxes 35
3.4. Extension 44
3.4.1 Cournot competition in the presence of horizontal differentiation 44
3.4.2 Bertrand competition 51
3.5. Concluding remarks 57
Appendices 59
A1. The effect of a change in the market structure on the difference in pre-tax industry profits between the two taxation regimes under Cournot competition 59
A2. The effect of a change in the market structure on the difference in consumer’s surpluses between the two taxation regimes under Cournot competition 61
B. The effect of a change in the market structure on the difference in pre-tax industry profits between the two taxation regimes under Bertrand competition 62
Chapter 4. The Superiority among Specific, Demand Ad Valorem and Cost Ad Valorem Subsidy Regimes 64
4.1. Introduction 64
4.2. Basic model 68
4.3. The industrial subsidy policy 69
4.3.1. Fixed number of firms 69
4.3.2. Free entry-and-exit 75
4.4. Export subsidy policies 81
4.5. Discussion 84
4.5.1. Introducing the domestic consumption into the third-country market model 84
4.5.2. The calibration of the amount of subsidy of the three subsidy policies 87
4.6. Concluding remarks 91
Appendix A. Proof of Proposition 1 92
Appendix B. Proof of Proposition 2 95
Appendix C. Proof of Proposition 3 96
Appendix D. Proof of Proposition 4 98
Chapter 5. Conclusion 102
References 104

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