本研究利用2003年至2008年間美國市場資料來探討公司股票購回所引起 的資訊效果，及公司與上下游商業對手之資訊不對稱程度的改變對公司股東財 富的影響。實證結果顯示公司在股票購回宣告後，本身的資訊不對稱程度會降 低，因此使公司股東的財富增加（資訊溢酬效果）。然而，在公司本身的資訊 不對稱程度降低的同時，亦提高了上下游商業交易對手的相對資訊優勢，此對 公司股東將造成負面影響。本研究發現相對資訊優勢效果會抵消因公司資訊不 對稱程度降低所帶來的資訊溢酬效果，此現象尤其在供應鏈上游更顯著。

Using U.S. data from 2003 to 2008, this study explores the information effects of the changes in information asymmetry of repurchasing firms and their business counterparties due to share repurchases on repurchasing firms’ stockholders’ wealth. We find that the information asymmetry of repurchasing firms decreases after repurchase announcements, which enhances their stockholders’ wealth (information premium effect). However, the information premium effect is offset by the relative information advantages gained by repurchasing firms’ business counterparties (relative information advantage effect), especially by their suppliers.

This study finds that a firm can use share repurchase as a signal to overcome the information asymmetry that exists between managers and stockholders, which benefits stockholders’ wealth (information premium effect). This information premium effect of share repurchases can be socially beneficial due to the reduction of information asymmetry risks and agency costs. In addition, the information flow in a supply chain is an important mechanism for business activities since a firm often benefits more by gaining information advantage relative to its business counterparties in business transactions. This decline in a repurchasing firm’s information asymmetry after a repurchase announcement causes the firm in a position of information disadvantage relative to its business counterparties, which impairs the firm’s stockholders’ wealth (relative information advantage effect). Therefore, a share repurchase action mitigates information asymmetry, which lowers a firm’s financing costs and provides positive news to the market, however, weakens the firm’s information advantage and enhances the bargaining powers of its suppliers and customers.