Audit sampling

　　Paper F8, Audit and Assurance and Paper FAU, Foundations in Audit require

　　students to gain an understanding of audit sampling. While you won’t be

　　expected to pick a sample, you must have an understanding of how the various

　　sampling methods work. This article will consider the various sampling

　　methods in the context of Paper F8 and Paper FAU.

　　This subject is dealt with in ISA 530, Audit Sampling. The definition of audit

　　sampling 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.’1

　　In other words, the standard recognises that auditors will not ordinarily test all

　　the information available to them because this would be impractical as well as

　　uneconomical. Instead, the auditor will use sampling as an audit technique in

　　order to form their conclusions. It is important at the outset to understand that

　　some procedures that the auditor may adopt do not involve audit sampling,

　　100% testing of items within a population, for example. Auditors may deem

　　100% testing appropriate where there are a small number of high value items

　　that make up a population, or when there is a significant risk of material

　　misstatement and other audit procedures will not provide sufficient

　　appropriate audit evidence. However, candidates must appreciate that 100%

　　examination is highly unlikely in the case of tests of controls; such sampling is

　　more common for tests of detail (ie substantive testing).

　　The use of sampling is widely adopted in auditing because it offers the

　　opportunity for the auditor to obtain the minimum amount of audit evidence,

　　which is both sufficient and appropriate, in order to form valid conclusions on

　　the population. Audit sampling is also widely known to reduce the risk of

　　‘over-auditing’ in certain areas, and enables a much more efficient review of

　　the working papers at the review stage of the audit.

　　In devising their samples, auditors must ensure that the sample selected is

　　representative of the population. If the sample is not representative of the

　　population, the auditor will be unable to form a conclusion on the entire

　　population. For example, if the auditor tests only 20% of trade receivables for

　　existence at the reporting date by confirming after-date cash, this is hardly

　　representative of the population, whereas, say, 75% would be much more

　　representative.

　　2

　　AUDIT SAMPLING

　　AUGUST 2011

　　SAMPLING RISK

　　Sampling risk is the risk that the auditor’s conclusions based on a sample may

　　be different from the conclusion if the entire population were the subject of the

　　same audit procedure.

　　ISA 530 recognises that sampling risk can lead to two types of erroneous

　　conclusion:

　　1. The auditor concludes that controls are operating effectively, when in

　　fact they are not. Insofar as substantive testing is concerned (which is

　　primarily used to test for material misstatement), the auditor may

　　conclude that a material misstatement does not exist, when in fact it

　　does. These erroneous conclusions will more than likely lead to an

　　incorrect opinion being formed by the auditor.

　　2. The auditor concludes that controls are not operating effectively, when in

　　fact they are. In terms of substantive testing, the auditor may conclude

　　that a material misstatement exists when, in fact, it does not. In contrast

　　to leading to an incorrect opinion, these errors of conclusion will lead to

　　additional work, which would otherwise be unnecessary leading to audit

　　inefficiency.

　　Non-sampling risk is the risk that the auditor forms the wrong conclusion,

　　which is unrelated to sampling risk. An example of such a situation would be

　　where the auditor adopts inappropriate audit procedures, or does not

　　recognise a control deviation.

　　METHODS OF SAMPLING

　　ISA 530 recognises that there are many methods of selecting a sample, but it

　　considers five principal methods of audit sampling as follows:

　　• random selection

　　• systematic selection

　　• monetary unit sampling

　　• haphazard selection, and

　　• block selection.

　　Random selection

　　This method of sampling ensures that all items within a population stand an

　　equal chance of selection by the use of random number tables or random

　　number generators. The sampling units could be physical items, such as sales

　　invoices or monetary units.

　　Systematic selection

　　The method divides the number of sampling units within a population into the

　　sample size to generate a sampling interval. The starting point for the sample

　　can be generated randomly, but ISA 530 recognises that it is more likely to be