Physically inspecting a sample of completed processing cycles for defective products provides direct evidence of the effectiveness of the quality control process. This method allows the internal auditor to observe firsthand whether defective products are being identified and removed prior to shipment, ensuring that the process operates as intended. This approach is more reliable than survey results or management reports, which may be subject to bias or inaccuracies.

The Institute of Internal Auditors (IIA) - Standards for the Professional Practice of Internal Auditing, Standard 2320 - Analysis and Evaluation