How Do I Determine My Audit Sample Size?
According to the Comptroller of the Currency, sampling is a method of utilizing scarce audit resources when the population of items to be tested is large. Although using knowledge and judgment to select a non-statistical sample is acceptable for many audit purposes, statistical sampling provides objectivity in sample selection and greater accuracy when drawing conclusions about the entire population of test items. Determining sample size takes some patience and the use of a calculator or statistical tables. An auditor must determine the test group’s population size and decide what confidence level and expected deviation rate are acceptable. Define the characteristics of items to be tested to determine the testing population size. Using common characteristics helps ensure that each item in the population has the same chance of selection. For example, the UK National Audit Office recommends using characteristics such as all items included in a payroll report on a given date, or all post
