The sampling method in which the entire sample is considered to be irregular if a single error is found is discovery sampling. Discovery sampling is a type of statistical sampling that is used to test for the existence of at least one occurrence of a specific characteristic or condition in a population. Discovery sampling is often used when the auditor expects the characteristic or condition to be very rare or nonexistent, and when any occurrence would have a significant impact on the audit objective. For example, discovery sampling can be used to test for fraud, noncompliance, or material misstatement.
Discovery sampling works by setting a very low tolerable error rate (the maximum rate of occurrence of the characteristic or condition that the auditor is willing to accept) and a high confidence level (the degree of assurance that the auditor wants to obtain). The auditor then selects a sample from the population using a random or systematic method, and examines each item in the sample for the presence or absence of the characteristic or condition. If no error is found in the sample, the auditor can conclude with a high level of confidence that the characteristic or condition does not exist or is very rare in the population. However, if one or more errors are found in the sample, the auditor cannot draw any conclusion about the population and must either expand the sample size or perform alternative procedures.
Discovery sampling differs from other sampling methods in that it does not allow for any errors in the sample. Other sampling methods, such as variable sampling, stop-or-go sampling, or judgmental sampling, can tolerate some errors in the sample and use them to estimate the error rate or amount in the population. However, discovery sampling is designed to test for zero-tolerance situations, where any error would be unacceptable or material. Therefore, discovery sampling considers the entire sample to be irregular if a single error is found.
References:
Audit Sampling - Overview, Purpose, Importance, and Types1
Audit Sampling - What Is It, Methods, Example, Advantage, Reason2
ISA 530: Audit sampling | ICAEW3
Audit Sampling - AICPA4
