method used to divide a population into homogeneous subgroups (strata). Each stratum is then sampled individually. The auditor may separately evaluate the sample results or may combine them to furnish an estimate of the characteristics of the total population. When very high- or low-value items are segregated into separate populations, each population is more homogeneous. A more representative sample can be derived from a relatively homogeneous population. Hence, fewer items need to be examined when several strata are examined separately than when the entire population is evaluated. Stratification improves the sampling process and enables auditors to relate sample selection to the materiality and turnover of items. Various audit procedures may be applied to each stratum, depending on the circumstances. An example of stratified sampling occurs when total accounts receivable (population) is divided into groups based on dollar balances for confirmation purposes. An illustration follows:
Stratification may not be by dollar amount only but also by type of transaction and by transaction frequency. Stratification is suggested when the characteristic under audit examination varies materially within different portions of the population. This approach is employed typically in variables sampling and often in attributes sampling.
