本文測試台灣股票上市公司股權結構及領導結構對股票報酬的影響。 過去的實證研究往往以公司治理的某單一層面探討其對公司表現的影響，這樣的做法乎略了所探討變數為其它變數的替代變數的可能性。 本文以1.)董事長是否兼任總經理，2.)董事人數，3.)管理階層持股以及4.)大股東持股等四個層面建立了一個公司治理指數。 以這個指數做為公司治理機制的衡量指標。 本文證實本指數是為公司治理有效的衡量指標，公司治理優者(指數高者)股價表現優於公司治理不佳者(指數低者)。
本文並以這個指數證實公司治理有效控管了管理階層對盈餘的管理。 公司治理不良者較傾向於以應計項目提高盈餘數字，而其報導小額盈餘以規避報導小額損失的可能也高於公司治理優良者，公司治理可有效減低盈餘管理而提升盈餘品質。

This paper tests the relationship between ownership/leadership structures and stock returns for firms listed in Taiwan. A “Governance Index” is built based on four different aspects of the company’s governance structure: 1.) CEO duality, 2.) Size of the board of directors, 3.) Managements’ shareholdings and 4.) Block shareholders’ holding. This index is used as a proxy measure of the effectiveness of corporate governance mechanism. I show that firms identified by the governance index as under sounding governance outperform those under poor governance. The results indicate that the corporate governance index built in this study is a valid measure in evaluating the effectiveness of corporate governance of firms in Taiwan.
I demonstrate one additional application of the governance index constructed in this dissertation by showing that firms (identified by the governance index) with strong corporate governance mechanism effectively constrain the propensity of managers to engage in earnings management and improve the quality of reported earnings. Corporate governance is an effective monitoring device of the quality of financial reporting. Firms with poor governance structure are more likely to avoid reporting small losses by reporting small positive earnings. Furthermore, the magnitude of abnormal accruals is significantly related to governance level. Firms with weak corporate governance structures are more likely to use discretionary accruals to raise reported earnings.

Contents
List of Tables ………… vi
1 Introduction ………… 1

2 Literature Review ………… 8
2.1 Board of directors …………8
2.2 CEO duality ………… 11
2.3 Ownership structure ………… 14
2.4 Corporate governance in Taiwan ………… 17

3 The Construction of the Governance Index ………… 20
3.1 The Index ………… 20
3.2 Discussion………… 27

4 Data and Descriptive Statistics ………… 30

5 The Validity of the Governance Index ………………… 34
5.1 The relation between governance index and the governance characteristics ………… 35
5.2 Market model analysis ………… 36
5.3 Governance index and the Fama-French model ……… 42
5.4 Discussions ………… 46

6 Corporate Governance Strength and Earnings Quality ………… 48
6.1 Introduction 48
6.2 Background………… 51
6.3 Variables and methodology ………… 56
6.4 Corporate governance as monitoring device of the quality of earnings ………… 59
6.5 Corporate governance and the quality of earnings ………… 67

7 Conclusion ………… 68
References …………71

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