Stratified

This sampling approach depends on dividing the items being tested into at least three groups: individually significant items, and an upper and a lower group of remaining items. A useful approach to stratification is to divide the remaining population after individually significant items into two groups based on the average item amount. Then, allocate the sample size two-thirds to the upper stratum (items above the average) and one-third to the lower stratum (items below the average).
If it is impractical to stratify after identifying individually significant items, the sample size is increased by 20%.The AICPA Sampling Guide notes that while sample sizes typically increase by 10% to 50% if the sample is not stratified, an adjustment of 100% or more may be needed when there is extreme variability in the characteristic of audit interest. If desired, you may apply a factor other than 20% by clicking the preview icon to view the sample size calculation.