核心代理問題(Central Agency Problem)與私有資訊交易(Informed Trading)，在台灣上市、櫃的公司層出不窮，也可以說家族或集團企業與私有資訊交易，是台灣資本市場的兩大特色。這兩大特色間，是否存在關聯性呢？這種情形是否能夠藉由一些公司治理的機制予以改善呢?這些問題都是資本市場的參與者、政府政策的制定者所共同關心的，也因此有許多學者投入相關研究。
本研究參考McInish 與Wood (1992)之作法，計算標準化買賣價差(Bid-ask Spread)，藉以衡量私有資訊交易(依變數)，並納入會影響買賣價差的控制變數，如交易量、個股風險、股價、公司規模、掛牌市場別，以避免買賣價差被這些因素干擾。採用La Porta、Lopez-De-Silanes、Shleifer 與Vishny (2002)的股份控制權(Voting Rights)與盈餘分配權(Cash Flow Rights)以及Claessens、Djankov 與Lang (2000)盈餘分配權佔股份控制權比率(盈餘股份比)的概念，使用1-盈餘股份比，亦即盈餘股份偏離率，來衡量核心代理問題。再導入公司治理相關的變數，如董事會規模、外部董事比率、法人持股比率、是否委託大型會計師事務所，將這些變數與盈餘股份偏離率相乘，即為核心代理問題與公司治理變數的互動項。藉由這些互動項與多元迴歸分析，本研究得以驗證核心代理問題引起的私有資訊交易，是否受到這些公司治理因素的控制。
依據本研究的分析結果，發現盈餘股份偏離率愈大，愈會有私有資訊交易的情形，而這種情形可透過增加董事會規模、委託大型會計師事務所查核，獲得抑制；但增加外部董事、外資持股比率則會加重之。

Family or group-owned corporations and informed trading are two features of Taiwan’s capital market. Is there any relationship between the two features? Can we solve this kind of problem by some mechanism of corporate governance? These issues are common concerns for participants of capital markets and government policy makers, therefore, there are many scholars devoting themselves in the related research.
This study adopts the work of McInish and Wood (1992), who measure informed trading by calculating standardized bid-ask spread. Moreover, some variables, such as trading volume, risk, stock price, company size, and listing market are taken into account because the literature indicates they may affect bid-ask spread. According to the concept of voting rights and cash flow rights introduced by La Porta, Lopez-De-Silanes, Shleifer, and Vishny (2002) and the concept of fraction of cash flow rights on the voting rights introduced by Claessens, Djankov, and Lang (2000), we use the difference ratio, which is one minus the fraction of voting rights over the cash flow rights, to measure the degree of central agency problems. The corporate governance variables, such as board size, the proportion of outside directors, and institutional shareholdings are employed as moderating variables. Multiple regression models are used to test the hypotheses.
According to the test results, we find that the more cash flow rights deviate from voting rights the more informed trading will be and it can be alleviated by increasing board size and hiring big CPA firms for audit purpose; while it can be worsen by adopting more outside directors and institutional shareholdings.

致謝詞.................................................................................................................. II
摘要......................................................................................................................III
ABSTRACT.........................................................................................................IV
目錄.......................................................................................................................V
圖目錄..................................................................................................................VI
表目錄..................................................................................................................VI
第一章 緒論..........................................................................................................1
第一節 研究背景與動機......................................................................................1
第二節 研究目的..................................................................................................2
第三節 研究範圍..................................................................................................2
第四節 研究流程..................................................................................................4
第二章 文獻探討與研究假說..............................................................................5
第一節 企業股權結構與核心代理問題之關係..................................................5
第二節 私有資訊交易相關文獻..........................................................................6
第三節 核心代理問題與私有資訊交易之關聯性..............................................8
第三章 研究設計................................................................................................15
第一節 研究架構................................................................................................15
第二節 研究樣本................................................................................................15
第三節 變數衡量................................................................................................16
第四節 驗證方式................................................................................................20
第四章 實證結果與分析....................................................................................22
第一節 樣本敘述性統計....................................................................................22
第二節 相關係數分析........................................................................................25
第三節 實證結果分析........................................................................................33
第四節 敏感性分析............................................................................................38
第五章 結論與限制............................................................................................40
第一節 研究結論與研究貢獻............................................................................40
第二節 研究限制與建議....................................................................................42
參考文獻.............................................................................................................43
中文部份.............................................................................................................43
英文部分.............................................................................................................44

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