Monetary Unit Sampling (MUS), also known as probability-proportional-to-size sampling, is a statistical technique that is primarily used to test for overstatements in account balances by giving larger-dollar items a higher chance of selection. This method is efficient for detecting material misstatements, especially in accounts where errors are more likely to occur in high-value transactions. MUS combines the advantages of stratified sampling and variable sampling, making it a preferred choice when auditors are concerned with the risk of overstatement in financial reporting.
For instance, an auditor reviewing a company’s accounts receivable balance of $5 million may apply MUS to test for validity. By sampling based on monetary units rather than the number of accounts, the auditor ensures that higher-value receivables, which pose greater risk, are more likely to be included in the sample. If the auditor finds that two of the sampled accounts are overstated by $5,000 each, these misstatements are projected to the entire population with statistical reliability. MUS is especially effective when few or no misstatements are expected, and it minimizes the number of items tested while maintaining high audit assurance. This method supports audit efficiency and risk-focused testing.