2007 年行政訴訟法及會計師法之修正，明定非律師為訴訟代理人，應得審判長之許可。此一修正招致會計師界的抗議，認為就稅務訴訟，會計師之專業知識不亞於律師。本文利用2005 年台北高等行政法院所得稅訴訟案件之判決書為樣本，以實證研究來檢驗訴訟代理人專業背景對訴訟效率與訴訟效果的影響。實證結果顯示，在訴訟效率部分，會計師的表現優於律師，能顯著縮短訴訟天數、節省法院及原告之經濟資源；在訴訟效果方面，則未有充分證據顯示律師與會計師間具有重大差異。但如忽略內生變數對研究的影響或僅比較勝訴機率在不同專業代理人間的分布情形，均易使研究訴訟效果的結論發生錯誤。

In 2007, an amendment to the Administrative Litigation Act and Certified Public Accountants Law required that a non-lawyer receive official permission from the presiding judge in order to act as an agent. The public accountants protested this amendment. According to their belief, accountants have adequate professional knowledge to act as an agent in litigation that involves tax administrative issues. This study uses empirical research, calling on the verdicts in 2005 from the Taipei High Administrative Court, to examine whether accountant-agents or lawyer-agents act more efficiently and/or effectively in litigation dealing with income-tax administration. Empirical evidence shows that public accountants perform more efficiently than lawyers, because litigation time period is significantly shorter for accountant-agents than for lawyer-agents. However, there is no significant difference in effectiveness between lawyer-agents and accountant-agents. Besides, the conclusion on the effectiveness can be spurious when research ignores endogenousity or simply compares the agents' probability of winning the case.