The internal auditor should use a procedure that directly tests the theory that shutdowns are due to outdated purchasing requirements not reflecting changes in production techniques. By comparing the parts needed according to current production estimates and the updated MRP with the purchase orders generated by the system, the auditor can determine if there are discrepancies indicating that the system is not correctly updating for new production methods. This approach ensures that the investigation is focused on the root cause of the issue and provides evidence to support any findings related to the suspected problem.
Reference:
Institute of Internal Auditors (IIA), International Standards for the Professional Practice of Internal Auditing (Standards), Standard 2310 - Identifying Information.