5. Basic Steps in a Statistical Plan
a. Determine the objectives of the plan.
1) For a test of controls, an example is to conclude that control is reasonably effective.
2) For a test of details, an example is to conclude that a balance is not misstated by more than an immaterial amount.
b. Define the population. This step includes defining the sampling unit (an individual item in the population) and considering the completeness of the population.
1) For tests of controls, the period covered is defined.
2) For tests of details, individually significant items may be defined.
c. Determine acceptable levels of sampling risk (e.g., 5% or 10%)
d. Calculate the sample size using tables or sample-size formulas.
1) In some cases, it is efficient to divide the population into subpopulations or strata. The primary objective of stratification is to minimize variability.
2) Stratification also allows the auditor to apply more audit effort to larger elements or more risky parts of the population.
3) For example, when auditing sales revenue, an auditor could divide the population into strata of dollar increments. The auditor could test transaction under us $500, between US $501 and US $2,000, and US $2,001 and above.
e. Select the sampling approach, e.g., random, interval, or block.
f. Take the sample. The auditor selects the items to be evaluated.
g. Evaluate the sample results. The auditor draws conclusions about the population.
h. Document the sampling procedures. The auditor prepares appropriate working papers.