The Public Company Accounting Oversight Board (PCAOB) issued a concept release in 2011 which proposes a mandatory audit firm rotation. However, PCAOB indicates that there is a limited amount of empirical data and research evidence on the potential costs and benefits of such mandatory audit firm rotation. This study provides some empirical evidences related to PCAOBs concerns. Specifically, we find that the largest clients audited by Big 4 accounting firms have few material internal control

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... esses and accounting restatements. In addition, accounting restatements are often reported within four years after the beginning of accounting errors and are reported by the same auditor during the restatement period. These findings cast doubt on the benefit of mandatory audit firm rotation. We also find that the largest audit clients on average represent over 20% of the audit revenues of local offices of Big 4 accounting firms. Thus, mandatory audit firm rotations could significantly disrupt the normal operations of public accounting firms if audit clients are required to change auditors periodically.