Reperformance is a CAATs approach that involves independently executing the same procedures as the original process to verify the accuracy of the application's calculations. This approach maximizes the use of CAATs because it directly tests the functionality and reliability of the system by ensuring that the system processes transactions and calculations correctly, as intended by management.
IIA References:
* IIA Standard 1220: Due Professional Care suggests that internal auditors should apply appropriate techniques, such as CAATs, to obtain sufficient evidence. Reperformance as a CAATs method is particularly effective in verifying the integrity of system calculations.
* The Practice Guide on Using CAATs highlights that reperformance is one of the most powerful techniques for validating that a system operates as intended and that transactions are processed correctly.

Demonstrating due professional care involves using appropriate technology and data analysis techniques to enhance the audit's effectiveness and efficiency. These tools help auditors identify anomalies, trends, and potential areas of risk more accurately and timely, reflecting a higher standard of care in their audit activities.
References:
"Auditing Standards and Guidelines," which emphasize the importance of using advanced techniques in audit processes.

According to the IIA's Implementation Guide for Standard 2340 - Engagement Supervision1, one of the activities that the chief audit executive or the designated engagement supervisor should perform is to review and approve the engagement work program before the commencement of fieldwork. The engagement work program should be based on the engagement objectives, scope, and approach, and should reflect the risks and controls identified during the planning phase. The engagement work program should also be discussed with the engagement team to ensure that they understand the tasks and procedures to be performed, and to address any questions or concerns. The engagement supervisor should document the approval of the work program and any subsequent changes in the workpapers.

Comprehensive and Detailed Explanation:
The auditor's goal is to test compliance with a set threshold (daily meal stipend). The most direct technique is compliance verification through data analytics (A), which compares actual expenses against policy limits.
Regression analysis (B) is used to identify correlations, not compliance with fixed limits. Gap testing (C) identifies missing values in sequences, not threshold violations. Flowcharts (D) document processes but do not test compliance. Therefore, the best approach is to use compliance analytics to flag all transactions exceeding the approved stipend, providing reliable evidence of policy adherence or violation.

Nonsampling risk is the risk that the auditor may reach incorrect conclusions for reasons not related to the sampling process, such as failure to recognize exceptions or misinterpretation of audit results. In this case, the internal auditor did not notice that some purchase requisitions were approved by unauthorized persons, which is an oversight unrelated to the sample size or selection process. This is distinct from sampling risk, which is the risk that the sample selected does not represent the population. References:
* The IIA's International Standards for the Professional Practice of Internal Auditing (Standards), Standard 2320 - Analysis and Evaluation.
* The IIA's Practice Guide on Audit Sampling.