公司規模效果最早是由Banz(1981) and Reinganum(1981)所提出，其發現在風險校正（risk-adjusted）之基礎下，小公司可賺取比大公司為高之報酬。然而，本研究之目的欲說明規模效果對於董監改選前持股不足之公司是否造成不同之股價反應。依照公司法第195條第一項『董事任期不得逾三年，但得連選連任』之規定每三年皆須改選一次董事，而改選之前若有持股不足者則將設法補足持股以尋求連任並避免股東常會之流會，然而，補足持股之方式可能因公司之規模大小不同而有所差異。Manne(1965)之研究發現，股權極端分散之公司，管理當局無法掌握大部份表決權，發生委託書爭奪戰之機率較高。DeAngelo(1988)則發現委託書爭奪戰通常發生於大型之公司。因此，我們推測大公司股權通常較小公司分散，股東人數較多且股價亦較高，故大部份公司董監可能以徵求委託書之方式來召開股東常會並尋求連任。而小公司則因股權相對大公司集中，股東人數較少且股價亦較低，故可能以自市場中購買股份之方式來順利召開股東常會並尋求連任。然而，大小公司補足持股之方式不同可能使股價產生不同之反應，故我們想知道此反應是否真的會因公司規模不同而有所差異？

　　基於上市公司的董監事為三年改選一次之規定，如果遇到該年將改選董監事，並且公司董監持股不足而進行補足持股之動作時，股價將可能有巨大漲幅，而此漲幅更會因公司規模越小而產生較大的異常報酬。因此本研究之主要目的在探討：

1.持股可能不足以連任之上市公司董監，會於董監改選前補足持股而對股價造成顯著之異常報酬?
2.持股不足之公司董監，補足持股之方式依公司規模而不同，使得小公司之異常報酬大於大公司?
3.持股不足之公司董監，補足持股之方式依公司股東人數而不同，股東人數愈少異常報酬應愈大?
4.持股不足且規模越小、持股比例越低者應有較高之異常報酬?
本研究之結論如下：

1.持股可能不足以連任之上市公司董監，會於董監改選前補足持股並使股價造成顯著之異常報酬。
2.持股不足之公司董監，補足持股之方式依公司規模而有所不同，異常報酬隨公司規模愈小而愈大。
3.除股東人數最少之投資組合（Q1）外，其餘投資組合隨著股東人數愈少而異常報酬愈大。
4.董監改選前，持股不足且規模越小、持股比例愈低者對股價造成之異常報酬較大。

　The firm size anomaly has puzzled researchers since it was first introduced by Banz(1981) and Reinganum(1981). Each found that on a risk-adjusted basis, small firms earned rates of return that exceeded those of larger firms. The purpose of this thesis is to document the existence of the firm size effect with respect to the electing of board when board’s ownership is not enough to renew the terms. According to Corporate Law, paragraph 195, section 1,” The tenure of boards cannot exceed three years, except for the terms of renewing.” The Board in one firm will manage to complement their ownership by the electing of board. However, ways of complementing ownership may depend on the firm size. Evidence by Manne(1965) indicates that the more dispersed the ownership of a firm, the higher probability of occurrence of proxy contest. DeAngelo(1988) states that proxy contests often occur in big firms. Hence, we infer that big firms often complement the board’s ownership by the way of occurring of proxy contest, due to the more dispersed ownership, the more shareholders, and the higher share price. Contrary to big firms, small firms often complement the board’s ownership by the way of purchasing the firm’s outstanding stocks, due to the less dispersed ownership, the fewer shareholders, and the lower share price. However, these two ways may result in different reactions to share price. We want to know if firm size effect exists.

　Described as the above, the board will complement their ownership by election and result in different reactions to share price. Thus, we test the following four hypotheses:

1.When board’s ownership is not enough to renew the terms, they will complement their ownership and cause significant abnormal returns?
2.The larger abnormal returns are observed on the date of stopping transferring ownership for small firms which board’s ownership is not enough to renew the terms?
3.The larger abnormal returns are observed on the date of stopping transferring ownership as the firms which board’s ownership is not enough to renew the terms has fewer shareholders?
4.Smaller firms which board’s ownership is not enough to renew the terms create the larger abnormal returns as the ownership is lower?

The conclusions are following:

1.When board’s ownership is not enough to renew the terms, they will complement their ownership and cause significant abnormal returns.
2.The larger abnormal returns are observed on the date of stopping transferring ownership for small firms which board’s ownership is not enough to renew the terms.
3.Except for the portfolio Q1, the others create larger abnormal returns on the date of stopping transferring ownership as the firms which board’s ownership is not enough to renew the terms has fewer shareholders.
4.Smaller firms which board’s ownership is not enough to renew the terms create the larger abnormal returns as the ownership is lower.

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