To determine the adequacy of the control's design for adding new vendors into the vendor contract system, a flowchart of the vendor addition process would be the most useful. A flowchart provides a clear and detailed visualization of the process, highlighting each step involved and the controls in place. This allows the auditor to assess whether the design of the control is appropriate and sufficient to mitigate relevant risks. While interviews, confirmations, and cost-benefit analyses provide useful information, they do not offer the same level of detailed insight into the control's design as a flowchart does.

Institute of Internal Auditors (IIA) - International Professional Practices Framework (IPPF)