The use of effective sampling procedures will improve the scope, focus and efficiency of audits and allow the auditor to provide assurance about the business processes that are relevant for the company to meet its goals and objectives.
From the point of view of the audit, sampling is the technique that allows the auditor to obtain conclusions from a set of elements (universe or population) through the study of a part that would be the sample. This is where the importance of using this tool lies, which allows us to obtain and see the reality in the operations of the company, and then formulate the appropriate conclusions regarding the population, from which the sample has been extracted.
The statistical sampling is executed by the auditor, either internal or external to the company, where he must design and select a sample, execute the audit procedures and evaluate the results of the same, to obtain sufficient, reliable, relevant and useful evidence , that allows to fulfill with the objectives of the audit.
So we can say that statistical sampling is the technique of great importance for the auditor, since it allows him to infer conclusions from a set of elements through the study of a sample, which can be complete or only a part of it, and thus Obtain evidence about certain characteristics of the population.
This sampling is used in both the compliance tests and the substantive tests. It is useful when the selection is a very large population and the characteristics of the items that are tested are not known. As it may be that the balance of an account is overvalued or diminished as a result of the application of amounts, incorrect prices or errors in calculations or sums.
It is important to note that there are several types of statistical sampling: statistical sampling and non-statistical sampling; of which we can recommend statistical sampling, since it contains different techniques that help to highlight the different areas to be audited. Thus we have: sampling by attribute, which the elements of the population and the sample are classified in two or more categories, according to a certain attribute or qualitative characteristic. Another is the sampling of monetary units, where the elements of the population are selected based on the monetary amounts. This means that the selection of a document depends on its monetary value
We also find random or probabilistic sampling, which can calculate in advance the probability of each of the samples, for possible selection.
Statistical sampling has the advantage for the auditor, which allows to formulate mathematically and measure the results with precision, increases the reliability of the information, saves time when analyzing the population, since it can be done in small samples, which leads to reduce costs.
To execute a statistical sampling plan in auditing, the following stages must be followed: firstly, the sample is planned and designed, it consists of examining the sample in detail, in order to obtain sufficient evidential evidence and to provide an objective basis for issuing its opinion. Then describe the specific objectives you want to achieve and the combination of procedures that can best contribute to achieving those objectives. Likewise, it will determine which situations constitute error, taking into account the objectives of the test. In general, when performing a compliance test, the auditor makes a preliminary assessment of the error rate expected from the population and the level of control risk. These preliminary assessments are useful for designing the sample and determining its size.
When performing the sample design, the auditor will choose the sample size, taking into account that it can be affected by the level of risk of sampling. The lower the acceptable level of risk, the larger the sample size should be. The size of the sample can be determined through the application of a statistical formula or through professional judgment, objectively applied to the circumstances. For this there are several methods, in which we have the sampling by attribute, where we estimate the proportion of a population with specific attributes and the sampling by monetary units which is the most appropriate, since the selection of the sample is made in function of the monetary amounts.
Another stage is the selection of the sample, the auditor must apply professional judgment to select the elements of the sample. Since the objective of sampling is to reach conclusions about the entire population, the auditor will try to select a representative sample by choosing elements that have the typical characteristics of the population, without introducing biases in the selection of the sample.
Finally, the auditor must evaluate the results of the sample to determine if these confirm or oblige to modify the preliminary evaluation of the characteristic of the population being sampled. If, upon analyzing the results, you conclude that you must review your initial evaluation of the population characteristic, which has been subject to verification, the auditor should request the management to investigate the errors identified and the possibility of more errors, recommending that make the necessary adjustments and / or modify the planned audit tests.
The evaluation of the results also depends on the professional judgment issued by the auditor, therefore the work must be documented to allow an efficient evaluation, as well as the justification of the conclusions.