ACCA F8 考试：AUDIT SAMPLING (Part 2)
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.
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 ‘truly’ random if the use of random number generators or random number tables are used. Consider the following example:
You are the auditor of Jones Co and are undertaking substantive testing on the sales for the year ended 31 December 2010. You have established that the ‘source’ documentation that initiates a sales transaction is the goods dispatch note and you have obtained details of the first and last goods dispatched notes raised in the year to 31 December 2010, which are numbered 10,000 to 15,000 respectively.
The random number generator has suggested a start of 42 and the sample size is 50. You will therefore start from goods dispatch note number (10,000 + 42) 10,042 and then sample every 100th goods dispatch note thereafter until your sample size reaches 50.
Monetary unit sampling
The method of sampling is a value-weighted selection whereby sample size, selection and evaluation will result in a conclusion in monetary amounts. The objective of monetary unit sampling (MUS) is to determine the accuracy of financial accounts. The steps involved in monetary unit sampling are to:
? determine a sample size
? select the sample
? perform the audit procedures
? evaluate the results and arriving at a conclusion about the population.
MUS is based on attribute sampling techniques and is often used in tests of controls and appropriate when each sample can be placed into one of two classifications – ‘exception’ or ‘no exception’. It turns monetary amounts into units – for example, a receivable balance of $50 contains 50 sampling units. Monetary balances can also be subject to varying degrees of exception – for example, a payables balance of $7,000 can be understated by $7, $70, $700 or $7,000 and the auditor will clearly be interested in the larger misstatement.
When the auditor uses this method of sampling, he does so without following a structured technique. ISA 530 also recognises that this method of sampling is not appropriate when using statistical sampling (see further in the article). Care must be taken by the auditor when adopting haphazard sampling to avoid any conscious bias or predictability. The objective of audit sampling is to ensure that all items that make up a population stand an equal chance of selection. This objective cannot be achieved if the auditor deliberately avoids items that are difficult to locate or deliberately avoids certain items.
This method of sampling involves selecting a block (or blocks) of contiguous items from within a population. Block selection is rarely used in modern auditing merely because valid references cannot be made beyond the period or block examined. In situations when the auditor uses block selection as a sampling technique, many blocks should be selected to help minimise sampling risk.
An example of block selection is where the auditor may examine all the remittances from customers in the month of January. Similarly, the auditor may only examine remittance advices that are numbered 300 to 340.
STATISTICAL VERSUS NON-STATISTICAL SAMPLING
Paper F8 students need to be able to differentiate between ‘statistical’ and ‘non-statistical’ sampling techniques. ISA 530 provides the definition of ‘statistical’ sampling as follows:
‘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.’ (2)
The ISA goes on to specify that a sampling approach that does not possess the characteristics in (i) and (ii) above is considered non-statistical sampling.
The above sampling methods can be summarised into statistical and non-statistical sampling as follows:
Statistical samplingNon-statistical sampling
Random samplingHaphazard sampling
Systematic samplingBlock selection
Monetary unit sampling
Statistical sampling allows each sampling unit to stand an equal chance of selection. The use of non-statistical sampling in audit sampling essentially removes this probability theory and is wholly dependent on the auditor’s judgment. Keeping the objective of sampling in mind, which is to provide a reasonable basis for the auditor to draw valid conclusions and ensuring that all samples are representative of their population, will avoid bias.
Paper F8 and FAU students must ensure they fully understand the various sampling methods available to auditors. In reality there are a number of ways in which sampling can be applied that ISA 530 recognises – however, the standard itself covers the principal methods.
Students must ensure they can discuss the results of audit sampling and form a conclusion as to whether additional work would need to be undertaken to reduce the risk of material misstatement.
Steve Collings is assessor for Paper F8
(1). ISA 530, paragraph 5 (a)
(2). ISA 530, paragraph 5 (g)
Last updated: 20 Apr 2015