Which sampling technique should an IS auditor use to determine the number of purchase orders not appropriately approved?

The appropriate sampling technique for determining the number of purchase orders not appropriately approved is attribute sampling. This technique is specifically designed for scenarios where the goal is to estimate the proportion of a population that meets a certain criterion, such as compliance with approval processes.

Attribute sampling allows the auditor to focus on specific attributes of the purchase orders, such as whether or not they have the necessary approvals. By selecting a sample of purchase orders and testing each one for the attribute of interest (proper approval), the auditor can calculate the rate of compliance within the sampled group. This information can then be used to project the overall compliance rate in the population of purchase orders.

This approach is advantageous in auditing contexts, particularly when the auditor is looking to evaluate the effectiveness of control processes and compliance with policies. It provides a clear structure for measuring non-compliance against defined approval criteria and is generally more efficient for this type of categorical assessment compared to other techniques like variable sampling, which would be more suitable for measuring quantities or amounts.