過去研究說明具產業專長之會計師仍能在客戶財務資訊不完整情況下，利用其行業特定知識與較高技術能力執行完善的審計工作(Thibodeau 2003; Moroney 2007; Hammersley 2006)。本論文定義資訊不確定性為客戶之財務資訊無法幫助預測公司的價值(Zhang 2006; Autore et al. 2009)。本論文推論若公司的財務報表具有不確定性會需要聘請產業專長會計師以減緩資訊不確定性的程度，並進一步研究具資訊不確定性公司若由非產業專長更換為產業專長會計師是否能提升其審計品質。由於審計工作目的在於提供資訊品質的確認(Dye 1993; Knechel et al. 2008)，審計人員會依據審計客戶的環境，設計和執行適當的審計計劃以減輕資訊不確定性情況。本論文以會計師角度建立一資訊不確定性架構，進一步將資訊不確定性分為基本價值波動不確定性與資訊品質不確定性，並推論產業專長會計師比較能在資訊品質不確定性中發揮其價值。本論文分為兩部分：第一部分檢驗資訊不確定性是否會影響產業專長會計師之選任，第二部分則檢測具資訊不確定性之審計客戶若選擇產業專長會計師之後，其審計品質是否會提升。 / Previous studies establish that a specialist auditor has more industry-specific knowledge and higher technological capability that can pertinently benefit situations in which client financial information is incomplete (Thibodeau 2003; Moroney 2007; Hammersley 2006). In this paper, we define information uncertainty as the ambiguity with respect to the implications of new information concerning a firm’s value (Zhang 2006; Autore et al. 2009). Because some financial statements present information in uncertain terms, we infer that companies whose financial statements provide uncertain information demand specialist auditors to alleviate the extent of information uncertainty. We further examine the improvements on audit quality made by those companies under information uncertainty which chose to switch from non-specialist auditors to specialist ones. As an assurance of information quality (Dye 1993; Knechel et al. 2008), an auditor, based on his knowledge of the auditee and its environment, will alleviate the uncertainty level of the auditee’s financial information through designing and executing an appropriate audit plan. We build a framework of information uncertainty and develop comprehensive measurements of information uncertainty from the auditor’s point of view. Moreover, this study disentangles the information uncertainty effects into fundamental volatility uncertainty and information quality uncertainty, and proposes that specialist auditors manifest their merits more under information quality uncertainty than under fundamental volatility uncertainty. In the first part of this study, we examine the auditors chosen by companies whose financial statements are characterized by information uncertainty. Previous studies on auditor choice address many reasons why companies switch their auditors (Lennox 2000; Carcello and Neal 2003; Blouin et al. 2007). Information uncertainty makes stakeholders lower their reliance upon company financials and even downgrade the filers, triggering negative stock price reactions (Merton 1987; Beneish et al. 2005; Beneish et al. 2008; Hammersley et al. 2008). Based on prior research, we can infer that a company under information uncertainty chooses to hire a specialist auditor to signal the credibility of the financial statements and improve market perception. We hypothesize that companies suffering uncertainty demand specialist auditors to alleviate their information uncertainty. The auditor’s information role is to ensure the reliability of financial information, and a specialist auditor is equipped with superior audit knowledge and technology. Therefore, we further infer that a company whose specific information uncertainty is attributable to information quality issues (rather than fundamental volatility issues) is more inclined to choose a specialist auditor. This is because a specialist auditor improves the credibility of financial information instead of being involved with the client’s business decisions. We use an auditor switching sample of U.S. companies from 2001-2009 to examine whether the information uncertainty is an issue of auditor choice or not. Consistent with our conjecture, companies under information uncertainty prefer to hire specialist auditors. Evidence partially supports that relative to companies under fundamental volatility uncertainty, companies suffering information quality uncertainty are more inclined to choose specialist auditors. In the second part of this study, we find evidence for the economic consequences of upgrading switches to a specialist auditor when the company is experiencing information uncertainty. After the Sarbanes-Oxley Act (hereafter, SOX), many companies began to take the cost-effect issue into consideration; they ultimately decided to go private (Zhang 2006; Engel et al. 2007) in order to avoid the high-cost of Section 404 or switch to a non-Big N audit firm (Calderon et al. 2007). There's no such thing as free lunch; the specialist auditor usually has greater ability and concomitant higher charges (Craswell et al. 1995; DeFond et al. 2000; Francis et al. 2005; Cahan et al. 2008). It is natural to question whether every company needs to engage specialist auditors if it has to pay high audit fees. In this paper, we attempt to determine in which circumstances specialist auditors can make a significant difference in improving audit quality. We investigate the relationship between auditor specialization and audit quality in an information uncertainty setting using an auditor switching sample taken from 2001 to 2009 in the United States. We examine ex post facto whether (1) specialist auditors improve audit quality more than their non-specialist counterparts; and (2) specialist auditors manifest their merits more under information quality uncertainty than the fundamental volatility uncertainty. Since the value of auditor industry specialization is reflected by the perceived and actual audit quality (Balsam et al. 2003; Nagy 2005), we examine both earnings response coefficient (ERC) and accruals quality to proxy audit quality (DAC). In both models, the audit quality of companies that suffer fundamental volatility uncertainty along with comprehensive uncertainty is not enhanced substantially following upgrade switching to a specialist auditor. We find strong empirical results that demonstrate companies under information quality uncertainty show significant improvements in audit quality after switching to specialist auditors. However, specialist auditors are significantly more capable of mitigating the information quality uncertainty than the fundamental volatility uncertainty. That is, auditor specialization is a critical solution when companies encounter information quality uncertainty.