Which control is MOST effective in ensuring that an unauthorized interest rate change is not processed?

The choice of managerial confirmation via an approval code is the most effective control to ensure that an unauthorized interest rate change is not processed. This control involves a higher-level verification system where a manager is responsible for approving any changes to interest rates. By requiring managerial involvement, the organization ensures that all modifications undergo scrutiny and are validated against company policies and regulatory requirements. This approach significantly mitigates the risk of unauthorized changes because it places an additional layer of oversight, increasing accountability and reducing the chance of errors or fraud.

The effectiveness of this control lies in its proactive nature; it not only addresses potential unauthorized changes but also reinforces the importance of the approval process within the organization. Ensuring that rates are not changed without appropriate managerial consent fosters a culture of compliance and diligence regarding financial operations.

In contrast, other options such as weekly reports of rate exceptions, while useful for monitoring, do not prevent unauthorized changes from occurring in real time. Similarly, having a clerk enter an approval code relies on the integrity and diligence of the clerk and does not provide an independent verification. Finally, a warning message displayed to the clerk might serve as a reminder but lacks the enforceability that a managerial review entails, making it less effective in preventing unauthorized actions.