法定公司所得稅稅率政策之決定因素－－國際租稅競爭或國內政治運作？

近期的租稅實證文獻認為影響一國公司所得稅稅率政策制定的因素除了國內經濟因素外，最主要的就是國際間的租稅競爭，而研究對象集中在歐盟或是OECD會員國等已開發國家；另政治經濟文獻雖強調政治才是決定租稅的最後關鍵因素，然而從事實證方面研究的文獻卻是極為有限，至今尚未涉及公司所得稅稅率，更未從事跨國研究。因此，不同於過去的租稅及政治經濟文獻，本文除探討來自他國的稅率競爭及經濟因素對一國之法定公司所得稅稅率的影響外，同時亦分析法定公司稅率是否受到政治運作如政府體制與貪腐等因素之干擾。樣本涵蓋不同開發程度之50個國家於1985－2007年間的追蹤資料，採用隨機效果模型來估計，結果得到法定公司稅率同時受到國際租稅競爭與政治因素的顯著影響。另外，開發程度越高的國家，對於稅率競爭壓力的反應越敏感。

Recent empirical literature on taxation, focusing mainly on countries in European Union or OECD countries, shows that the most important factor affecting a country's income tax rate policy, besides domestic economic factors, is international tax competition. Studies on political economics, though emphasizing the importance of politics in determining taxation, provide little empirical cross country evidence on this issue. This paper investigates the impact of tax competition and economic factors on domestic corporate tax rates. We also examine the link between corporate tax rates and political factors, such as the level of corruption and the role of parliamentary system. Using annual data of 50 countries, covering developed and developing countries, from 1985 to 2007, we show that domestic corporate tax level is affected significantly by tax rates in neighboring countries, the degree of political corruption, and the proper functioning of parliamentary system. The results also suggest that pressure from tax competition is more intense for developed countries.