間接網路外部性對租稅歸宿之影響

Abstract

根據Katz and Shapiro（1985）的定義，間接網路外部性指一個產品的消費者效用會隨著另一個產品消費者人數的增加而提高。本文拓展Armstrong（2006）邊際成本固定、服務兩個市場1、2的獨佔平台生產者模型，討論若對平台市場1課利潤稅或從價稅（銷售稅），間接網路外部性如何影響租稅轉嫁。結果發現：不論利潤稅或從價稅，首先，平台會藉由調降市場1稅後均衡價格、增加市場2稅後均衡價格，以將租稅旁轉至市場2的方式賺取更多利潤。其次，市場2承受的租稅負擔隨市場1稅後均衡人數越多而越多，並且除了兩市場人數增加的情況無法確定外之外，均有超額轉嫁的可能。最後，在從價稅發現，當市場1彈性小，平台需要調降越多市場1價格以刺激市場1需求，市場1稅後人數因此增加，使平台越能夠拉抬市場2價格，此與過去彈性理論指出彈性越小者會承擔越多租稅的結果不一致。

According to Katz and Shapiro (1985), indirect network externality means the number of consumers of one product being an increasing function of the number of consumers of another product. This paper utilizes the model in Armstrong (2006) to discuss tax shifting when a constant marginal cost monopolistic platform producer serves two markets in the existence of indirect network effect. The results show that either market 1 is taxed by profits or by an ad valorem tax (sales tax), the price of market 1 reduces and the price of market 2 increases. By shifting the tax to market 2, the platform earns more profits when market 1 is taxed. The tax burden of market 2 depends on the after-tax number of consumers in market 1. A larger number of consumers in market 1 after taxation, results in more tax burden been shifted to market 2. In most cases, there exists excessive tax-shifting except when both markets have more consumers after taxation. Finally, with an ad valorem tax, if the demand elasticity of market 1 is small, the platform needs to downward adjusting market 1’s price more so that to increase the demand in market 1. A lower price in market 1 results in more consumers in market 1, and the platform gets easier to raise the price of market 2; this is at odds to the previous result that a smaller elasticity implies more tax burden.