自美國安隆案與台灣博達案先後爆發企業舞弊案件，對資本市場造成重大 衝擊，為了健全資本市場，確保投資大眾權益，各國證券主管機關希望藉由實 施會計師輪調制度來改善審計品質。本研究利用我國上市櫃公司2000年至2003 年兩千多筆資料，以異常應計數絕對值做為盈餘管理程度的代理變數，檢視兩 個研究議題：(1)以傳統OLS迴歸模型分析我國會計師事務所任期長短與盈餘管 理程度之關係；(2)運用自我選擇模型，重新檢驗會計師事務所任期與盈餘管理 程度之關係，並與傳統迴歸分析結果做一比較。研究結果發現，以傳統OLS迴 歸分析，顯示會計師事務所任期與盈餘管理程度具有顯著的負向關係，但此一 負向關係在自我選擇模型下則較不顯著。此結果之含意為，會計師事務所任期 愈長應不致使審計品質變差，但也未必能提昇審計品質。

Following many events on accounting scandals such as Enron case in USA and Procomp Informatics case in Taiwan, the capital market has suffered a major impact. To better upkeep the market and to safeguard the interest of public investors, many government regulators are hoping to improve the audit quality by the mechanism of mandatory auditor rotation. Based on the financial data from year 2000 to 2003 of the listed companies in Taiwan, this study uses over 2,000 firm/year observations to examine two issues: (1) if the audit firm tenure relates to the level of earnings management, proxied by the absolute value of abnormal accruals; (2) if the association between the audit firm tenure and earnings management remains unchanged with the use of “Self-selection” model instead of traditional OLS regression model. Our empirical result shows that the audit firm tenure is significantly negatively related to the level of earnings management from traditional OLS regression, however this relation becomes less significant under the self-selection model. This evidence implies that longer audit firm tenure does not necessarily cause the deterioration and/or improvement of audit quality.