本文檢視經理人過度自信是否改變經理人持股對公司價值的影 響，以Tobin’s Q 衡量公司價值，1997 年至2014 年台灣上市櫃公司 年資料的迴歸分析發現，經理人持股對公司價值之影響在經理人無 過度自信時呈U 型；若不考慮持股率平方項則為正斜率線形；若經 理人過度自信，則為倒U 型或無顯著關係。使用四種過度自信指標、 考慮經理人持股及過度自信之內生性後，此結果仍然不變。再者， 經理人持股低時，有無過度自信並未使公司價值顯著不同，乃因過 度自信對已相對低的價值衝擊有限。故證據支持經理人與股東利益 一致與過度自信假說，不符合職位防衛假說。本文也發現經理人過 度自信導致其高持股亦無助提升公司價值與不當投資有關，因為高 持股和過度自信時，投資對現金敏感性相對較高。

This article examines whether managerial overconfidence alters the impact of managerial ownership on firm value. With a sample encompassing annual data of Taiwan’s listed and OTC companies for the period 1997–2014 and using Tobin’s Q as firm value, the results from regression analyses indicate that under the situation of no overconfidence by managers, the effect of managerial ownership on firm value follows a U-shaped pattern, but there is a positive-slope linearity if squared ownership is not considered. However, if managers are overconfident, then ownership value exhibits either an inverse U-shaped curve or an insignificant relationship. The results are unchanged even after iterations with four indicators for managerial overconfidence and by considering the endogeneity of both ownership and overconfidence. Moreover, when managers have low ownership, their overconfidence does not make a significant difference in firm value, because it has limited harm on any relatively low value. Therefore, the hypothesis of convergence of interests for managers and shareholders and the overconfidence hypothesis both hold, but the entrenchment hypothesis does not. This article also uncovers one reason, related to improper investments, for why managers with high ownership and overconfidence fail to raise firm values due to the relatively high sensitivity of cash flows to investments.