本研究的主要目的為探討公司宣告購回股數佔其流通在外股數比例和實際 購回佔其宣告購回股數的比例兩者與股票市場中異常報酬的關係，以及公司實際 購回佔其宣告購回股數的比例是否受到宣告之後的異常報酬影響，也就是公司管 理者是否會策略性的進行實際購回，此外也探討不同規模(市值)與不同實際購回 比例的公司其宣告購回比例與異常報酬的關係。
如果公司宣告買回股票的比例與市場反應（異常報酬）有顯著關係，表示宣 告 購 回 股 票 具 有 資 訊 內 涵 （ Comment and Jarrell 1991 ； Ikenberry and Vermaelen 1996）；相反的，若實際購回股票比例與市場反應有顯著的關係，而 宣告買回股票比例與市場反應沒有顯著關係，則表示市場反應的資訊內涵係來自 實際購回而非宣告購回，同時也代表投資人能夠對公司的實際購回多寡進行理性
宣告購回率/實際購回率 高 中 低
高 1.472*** 0.914 3.941**
中 1.089 0.242 -3.950
低 -24.494** -16.418 -2.524 所有 1.741** 0.885 1.637*
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預期（Stephens and Weisbach 1998）。而管理者有可能策略性的應用實際購回 額度，比如可能視其宣告前股價被低估的程度以及宣告期間股價回升幅度來決策 國市場不同（Stephens and Weisbach 1998），代表台灣的投資人普遍而言還無 法對實際買回的數量做出有效預期，其原因可能是，跟美國相比，台灣的散戶投
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異常報酬與其宣告購回比例之間的顯著關係之後，可以利用購回股票的宣告來進 行策略性投資。
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