Reasonable Assurance   SEC & PCAOB > PCAOB > Auditing Standard No. 2 > The Concept of Reasonable Assurance Source: PCAOB Release 2004-001 March 9, 2004 Page A–13 – Standard The Concept of Reasonable Assurance 17. Management's assessment of the effectiveness of internal control over financial reporting is expressed at the level of reasonable assurance. The concept of reasonable assurance is built into the definition of internal control over financial reporting and also is integral to the auditor's opinion.4/ Reasonable assurance includes the understanding that there is a remote likelihood that material misstatements will not be prevented or detected on a timely basis. Although not absolute assurance, reasonable assurance is, nevertheless, a high level of assurance. 18. Just as there are inherent limitations on the assurance that effective internal control over financial reporting can provide, as discussed in paragraph 16, there are limitations on the amount of assurance the auditor can obtain as a result of performing his or her audit of internal control over financial reporting. Limitations arise because an audit is conducted on a test basis and requires the exercise of professional judgment. Nevertheless, the audit of internal control over financial reporting includes obtaining an understanding of internal control over financial reporting, testing and evaluating the design and operating effectiveness of internal control over financial reporting, and performing such other procedures as the auditor considers necessary to obtain reasonable assurance about whether internal control over financial reporting is effective. 19. There is no difference in the level of work performed or assurance obtained by the auditor when expressing an opinion on management's assessment of effectiveness or when expressing an opinion directly on the effectiveness of internal control over financial reporting. In either case, the auditor must obtain sufficient evidence to provide a reasonable basis for his or her opinion and the use and evaluation of management's assessment is inherent in expressing either opinion. Note: The auditor's report on internal control over financial reporting does not relieve management of its responsibility for assuring users of its financial reports about the effectiveness of internal control over financial reporting. 4/ See Final Rule: Management's Reports on Internal Control Over Financial Reporting and Certification of Disclosure in Exchange Act Periodic Reports, Securities and Exchange Commission Release No. 33-8238 (June 5, 2003) [68 FR 36636] for further discussion of reasonable assurance.