Audit sampling as defined by ISA 530 is “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.”
The means available to the auditor for
selecting items for testing are;
- Selecting all items (100% examination)
- Selecting specific items; and
- Audit Sampling
Audit sampling can be applied using
either non-statistical or statistical sampling approaches.
Statistical approach has the following
characteristics:
- Random selection of the sample items; and
- The use of probability theory to evaluate sample results, including measurement of sampling risk.
A sampling approach which does not possess
the above characteristics is called non-statistical sampling.
Steps in planning the sample are as
follows:
- Determining the objectives of the test;
- Defining what errors or deviation are being sought;
- Identifying the population and sampling units; and
- Deciding the size of the sample.
Generally, larger the size
of the sample, the more it will be representative of a population. Many audit firms would like to
standardize the size of sample based on general and specific risk factors. Errors
increase the imprecision of results from sampling. Therefore, if they are expected,
a larger sample size is required. Finally in evaluating misstatements, the
auditor, should exclude ‘anomalous’ error(s) which are misstatement or
deviation that are demonstrably not representative of misstatements or deviations
in a population from his projected misstatements. However, such errors may be
considered when evaluating all misstatements within the sample and auditors
shall obtain sufficient appropriate audit evidence to corroborate the fact that
an error or deviation is anomalous.
Practice
Auditors need to consider
the specific objectives to be achieved and the combination of audit procedures
that is most likely to achieve those objectives. Audit sampling is applicable
to both tests of control and substantive procedures.