Tolerable error is the maximum error in the population that the auditor would be willing to accept and still concludes that the result from the sample has achieved the audit objective. Tolerable error is considered during the planning stage and, for substantive procedures, is related to the auditor’s judgement about materiality. The smaller the tolerable error, the greater the sample size will need to be. In tests of control, the tolerable error is the maximum rate of deviation from a prescribed control procedure that the auditor would be willing to accept, based on the preliminary assessment of control risk. In substantive procedures, the tolerable error is the maximum monetary error in an account balance or class of transactions that the auditor would be willing to accept so that when the results of all audit procedures are considered, the auditor is able to conclude, with reasonable assurance, that the financial statements are not materially misstated.
If the auditor expects error to be present in the population, a larger sample than when no error is expected ordinarily needs to be examined to conclude that the actual error in the population is not greater than the planned tolerable error. Smaller sample sizes are justified when the population is expected to be error free. In determining the expected error in a population, the auditor would consider such matters as error levels identified in previous audits, changes in the entity’s procedures, and evidence available from other procedures