本篇論文研究期間為在2006年之間宣告盈餘警示的上市公司，共777個樣本，研究集中程度不同之公司是否存在不同程度之資訊不對稱。透過市場對盈餘警示之反應、公司投資機會與公司營運狀況，推論出集中度越高之公司存在較為嚴重之資訊不對稱問題。本研究將樣本分為正面警示與負面警示進行檢定，結果顯示當公司發布警示時，市場在事件窗口(-1,2)期間有顯著的反應，正面警示有顯著為正之累績異常報酬，負面警示則伴隨顯著為負之累績異常報酬。本研究發現，集中公司所發布的警示將引起市場較激烈之反應，無論集中公司發布正面警示或是負面警示皆存在此一現象，而藉由此現象可推論集中度高之公司應存在較嚴重之資訊不對稱問題。公司的資訊不對稱程度，對公司的對外投資機會與公司的營運績效亦有顯著的影響。本研究顯示，多角化公司在盈餘警示之後，在公司對外投資機會與公司營運績效兩方面皆有較佳的表現。跟據過去的文獻，投資機會與營運績效的改善皆可能來自於公司較低的資訊不對稱。故本研究推論，在盈餘警示之後，集中度高之公司仍然存在較多角化公司嚴重之資訊不對稱問題。實証結論顯示集中公司在盈餘警示前後皆存在較多角化公司嚴重的資訊不對稱問題。 This study contains 777 firms who announce earnings warnings, and analyzes information asymmetry problem among firms with different corporate structures by examining market response to earnings warning, investment opportunities and operating performance. The results indicate firms with higher level of focus will have more severe information asymmetry problem. Market will response to firms’ earnings warnings in the (-1, 2) event window. Significant positive CAR surrounds positive warnings, and significant negative reaction surrounds negative warnings. We find market will react more drastically to earnings warning announced by focused firms no matter the warning is positive or negative, and this phenomenon can be due to higher information asymmetry for focused firms. Severity of information asymmetry will also have significant impact on firms’ investment opportunities and operating performance. As shown in this study, diversified firms will gain better investment opportunities and better operating performance after earnings warnings. Based on previous literatures, the improvement of investment opportunities and operating performance may come from the lower information asymmetry, so we infer the focused firms will still have more severe information asymmetry problem after earnings warning. Overall, empirical results in this study suggest that focused firms suffer more information asymmetry problem than diversified firms before and after earnings warning.
