What is the most effective sampling method to ensure purchase orders are authorized according to an authorization matrix?

The most effective sampling method for ensuring that purchase orders are authorized according to an authorization matrix is attribute sampling. This method is particularly well-suited for assessing whether specific characteristics or attributes of a population meet predetermined criteria, such as the presence of proper authorization.

In this context, attribute sampling allows the auditor to select a sample of purchase orders and determine whether each order is authorized according to the specified matrix. The focus is on identifying compliance with the authorization requirement rather than measuring the extent of monetary value, which aligns with the objective of verifying adherence to controls.

By using attribute sampling, auditors can estimate the rate of authorization compliance within the population of purchase orders, making it a targeted approach for testing whether the controls in place are operating effectively. This method provides a clear pass/fail outcome for each sampled item, thereby simplifying the analysis of compliance with the authorization policy.

Other methods, like variable sampling or stratified mean per unit, are generally used for estimating numerical values or means rather than assessing the compliance with specific attributes. Consequently, they would not provide the same clarity or focus on authorization adherence as attribute sampling does, making them less effective for this particular objective.