2005年8月30日行政院發佈所得基本稅額條例草案,該條例於同年12月12日在立法院三讀通過,明確列示有關「最低稅負制」之各種事項,於2006年1 月1日開始正式實施,為我國所得稅課徵的制度開啟了全新的一頁。本研究將藉由檢視四個與所得基本稅額條例相關之事件日,採事件研究法分析於所得基本稅額條例相關事件日有無顯著之累積異常報酬率產生,並藉由比較公司享受租稅優惠的程度,以探討所得基本稅額條例是否確實造成公司股價下跌,並在有無享受租稅優惠之公司間下跌的程度會有所差異。 實證結果顯示支持本研究假說,即有享受租稅優惠之公司較未享受租稅優惠之公司有較大的負向股價報酬,累積異常報酬率多元迴歸所得的結果亦支持本研究假說。因此,享受租稅優惠程度高對所得基本稅額條例相關事件日所產生之負向累積異常報酬率較為顯著,且享受租稅優惠程度高的公司較其它沒有享受租稅優惠的公司所受到最低稅負制之影響更為強烈。
The Alternative Minimum Tax Act (AMT), drafted by the Executive Yuan on August 30, 2005 and passed its third reading in the Legislative Yuan on December 12 the same year, was implemented on January 1, 2006. AMT regulated specifically minimum tax burden representing a new era in Taiwan’s income tax history. This study uses event study to ascertain the existence of cumulative abnormal returns throughout four critical dates relating to the AMT. Through the analysis of the differences in the corporate tax rate under AMT, this study investigates the impact of AMT on stock prices. Empirical evidences support this study’s hypothesis that corporations who enjoyed relatively more favorable tax rates have greater negative impact on stock prices under AMT. The results of multiple regression analysis of cumulative abnormal returns also confirm that AMT event dates have significantly greater negative cumulative abnormal return for corporations enjoyed favorable tax rates, and the negative impacts are positively related to the level preferable tax treatment.