一般化的最適差別關稅原則

Abstract

傳統探討最適差別關稅議題的貿易文獻忽略兩個重要的現象，一是租稅制度對貿易政策的影響，二是僅探討兩個單一的出口國。有鑑於此，本文在傳統文獻中導入公司稅制，並將其擴展至兩個出口的廠商群而非兩個出口的單一廠商。在此一設定之下，我們獲得了一個較一般化的課稅原\\r則，亦即，最適差別關稅的政策應修正為對高平均的有效邊際成本課徵較低的關稅；而傳統「高（低）成本、低（高）關稅」的課稅原則，僅是本文的一個特例。此外，由本文獲致的結果可知，最適的差別關稅不必然應該對生產效率較高的廠商群課徵較高的關稅，必須視這兩個不同的廠商群的租稅環境而定；當生產效率較低的廠商群所面對的租稅環境使得其平均的有效邊際成本低於生產效率較高的廠商群時，反而應該對其課徵較低的關稅。較特別的是，即使兩個出口的廠商群的成本相同，只要其租稅環境不同，仍然應該課徵差別關稅；而且有效稅率較低的出口群其關稅稅率應愈重。

Apart from the traditional literature on optimum policy of discriminatory tariffs, this paper establishes a more general model that includes the home country’s domestic tax system and multi export country groups. Under the setup, we find that the traditional result is only a special case of this general model and should be refined. The new result is that the export product with a lower “effective” cost should be imposed a higher import tariff. As long as the tax environment factors are considered, however, the result might not hold. When firms with higher product costs face a tax environment that makes theiraverage effective product cost lower than the firms with lower product cost, the tariff rate for the former group should be higher. It is important to note that even if the two export groups have exactly the same product cost, imposed discriminatory tariffs are necessary if the tax policy they face are different; the lower the effective tax rate, the higher the tariff rate should be.