ISA 530 – Scope
This ISA complements ISA 500, which deals with the auditor’s responsibility to design and perform audit procedures to obtain sufficient appropriate audit evidence to be able to draw reasonable conclusions on which to base the auditor’s opinion. ISA 500 provides guidance on the means available to the auditor for selecting items for testing, of which audit sampling is one means.
ISA 530 – Objective
The objective of the auditor, when using audit sampling, is to provide a reasonable basis for the auditor to draw conclusions about the population from which the sample is selected.
ISA 530 – Definitions
For purposes of the ISAs the following terms have the meanings attributed below:
- Audit sampling: The application of audit procedures to less than 100% of items within a population of audit relevance such that all sampling units have a chance of selection in order to provide the auditor with a reasonable basis on which to draw conclusions about the entire population.
- Population: The entire set of data from which a sample is selected and about which the auditor wishes to draw conclusions.
- Sampling risk: The risk that the auditor’s conclusion based on a sample may be different from the conclusion if the entire population were subjected to the same audit procedure. Sampling risk can lead to two types of erroneous conclusions:
a. In the case of a test of controls, that controls are more effective than they actually are, or in the case of a test of details, that a material misstatement does not exist when in fact it does. The auditor is primarily concerned with this type of erroneous conclusion because it affects audit effectiveness and is more likely to lead to an inappropriate audit opinion.
b. In the case of a test of controls, that controls are less effective than they actually are, or in the case of a test of details, that a material misstatement exists when in fact it does not. This type of erroneous conclusion affects audit efficiency as it would usually lead to additional work to establish that initial conclusions were incorrect.
- Non-sampling risk: The risk that the auditor reaches an erroneous conclusion for any reason not related to sampling risk.
- Anomaly: A misstatement or deviation that is demonstrably not representative of misstatements or deviations in a population.
- Sampling unit: The individual items constituting a population.
- Statistical sampling: An approach to sampling that has the following characteristics:
i. Random selection of the sample items; and
ii. The use of probability theory to evaluate sample results, including measurement of sampling risk.
A sampling approach that does not have characteristics (i) and (ii) is considered non-statistical sampling.
- Stratification: The process of dividing a population into sub-populations, each of which is a group of sampling units which have similar characteristics (often monetary value).
- Tolerable misstatement: A monetary amount set by the auditor in respect of which the auditor seeks to obtain an appropriate level of assurance that the monetary amount set by the auditor is not exceeded by the actual misstatement in the population.
- Tolerable rate of deviation: A rate of deviation from prescribe internal control procedures set by the auditor in respect of which the auditor seeks to obtain an appropriate level of assurance that the rate of deviation set by the auditor is not exceeded by the actual rate of deviation in the population.
Sample Design, Size, and Selection of Items for Testing
When designing an audit sample, the auditor shall consider the purpose of the audit procedure and the characteristics of the population from which the sample will be drawn.
The auditor shall determine a sample size sufficient to reduce sampling risk to an acceptably low level.
The auditor shall select items for the sample in such a way that each sampling unit in the population has a chance of selection.
Performing Audit Procedures:
The auditor shall perform audit procedures, appropriate to the purpose, on each item selected.
If the audit procedure is not applicable to the selected item, the auditor shall perform the procedure on a replacement item.
If the auditor is unable to apply the designed audit procedures, or suitable alternative procedures, to a selected item, the auditor shall treat that item as a deviation from the prescribed control, in the case of tests of controls, or a misstatement, in the case of tests of details.
Nature and Cause of Deviations and Misstatements:
The auditor shall investigate the nature and cause of any deviations or misstatements identified, and evaluates their possible effect on the purpose of the audit procedure and on other areas of the audit.
In the extremely rare circumstances when the auditor considers a misstatement or deviation discovered in a sample to be an anomaly, the auditor shall obtain a high degree of certainty that such misstatement or deviation is not representative of the population. The auditor shall obtain this degree of certainty by performing additional audit procedures to obtain sufficient appropriate audit evidence that the misstatement or deviation does not affect the remainder of the population.
For tests of details, the auditor shall project misstatements found in the sample to the population.
Evaluating Results of Audit Sampling:
The auditor shall evaluate:
- The results of the sample; and
- Whether the use of audit sampling has provided a reasonable basis for conclusions about the population that has been tested.