SAMPLING DALAM
PENGUJIAN PENGENDALIAN
Konsep Dasar
AU 350.01 defines audit sampling as the application of an audit
procedure to less than 100% of the items within an account
balance or class of transactions for the purpose of evaluating
some characteristics of the balance or class.
Audit sampling is applicable to both tests of controls and
substantive tests. However, it is not equally applicable to all the
auditing procedures that may used in performing these tests.
Risiko Sampling
When sampling is used in meeting the second and third standards
of fieldwork, it should be recognized that uncertainties may result
from factors:
1. Associated directly with the use of sampling (sampling risk) and
2. Unrelated to sampling (nonsampling risk).
Sampling risk relates to the possibility that a properly drawn
sample may not be representative of the population.
Risiko Sampling dalam Test of Control
The risk of assessing control risk too low is the risk that the
assessed level of control risk based on the sample supports the
planned assessed level of control risk when the true operating
effectiveness of the control structure policy or procedure, if
known, would not be considered adequate to support the
planned assessed level.
The risk of assessing control risk too high is the risk that the
assessed level of control risk based on the sample does not
support the planned assessed level of control risk when the true
operating effectiveness of the control structure policy or
procedure, if known, would be considered adequate to support
the planned assessed level.
Risiko Sampling dalam Substantive Test
The risk of incorrect acceptance is the risk that the sample
supports the conclusion that the recorded account balance is not
materially misstated when it is materially misstated.
The risk of incorrect rejection is the risk that the sample supports
the conclusion that the recorded account balance is materially
misstated when it is not materially misstated.
Risiko Nonsampling
Nonsampling risk refers to the portion of the audit risk that is not
due to examining only a portion of the data. Sources of
nonsampling risk include:
1. Human mistakes, such as failing to recognize errors in
documents,
2. Applying auditing procedures inappropriate to the audit
objective,
3. Misinterpreting the results of a sample, and
4. Relying on erroneous information received from another
party, such as an erroneous confirmation response.
Pendekatan Sampling - Statistical and Nonstatistics
Attribute Sampling dan Variable Sampling
An auditor may use sampling to obtain information about many
different characteristics of a population. However, most audit
samples lead either to an estimate of:
1. a deviation rate or
2. a dollar amount.
When statistical sampling is used, these sampling techniques are
identified as attribute sampling and variables sampling,
respectively.
Attribute Sampling dan Variable Sampling
Sampling
Techniques
Type of
Test
Purpose
Attribute sampling
Test of controls
To estimate the rate of deviations from
prescribed controls in a population
Variables sampling
Substantive test
To estimate the total dollar amount of a
population or the dollar amount of error in a
population
Nonstatistical Sampling
The steps involved in a nonstatistical sampling plan include the
following:
1. Determine the audit objectives and procedures to meet the
objectives.
2. Define the population and sampling unit.
3. Specify the control of interest and evidence that the control
was effective or ineffective.
4. Use professional judgment to determine sample size.
5. Use professional judgment to determine the sample selection
method.
6. Apply audit procedures for tests of controls.
7. Evaluate the sample results.
Statistical Sampling
The steps in a statistical sampling plan for tests of controls are as
follows:
1. Determine the audit objectives.
2. Define the population and sampling unit.
3. Specify the attributes of interest.
4. Determine the sample size.
5. Determine the sample selection method.
6. Execute the sampling plan.
7. Evaluate the sample results.
Attributes dalam Pengendalian
Attribute
Description of Attribute
1.
Existence of sales invoice copy with supporting shipping document, sales
order, and customer order.
Authorization of sale by appropriate sales order department personnel.
Sales order department verification of agreement of sales order with
customer order as to quantities, descriptions, and prices.
Approval of credit by authorized credit department personnel.
Shipping department verification of goods shipped with sales order.
Billing department verification of agreement of sales invoice with shipping
document and sales order.
Billing department verification of pricing and mathematical accuracy of
sales invoice.
Agreement of details of sales journal and subsidiary ledger entry with sales
invoice.
2.
3.
4.
5.
6.
7.
8.
Sampling Statistik
In order to determine a sample size for each attribute or control
to be tested, the auditor must specify a numerical value for each
of the following factors:
1. Risk of assessing control risk too low
2. Tolerable deviation rate
3. Expected population deviation rate
Sampling Statistik
Factor
Relationship to
Sample Size
Risk of assessing control risk too low
Inverse
Tolerable deviation rate
Inverse
Expected population deviation rate
Direct
Population size
Increases above 5,000 units
Fewer than 5,000 units
No effect
Direct
Random Sampling
When selecting a random sample, it is possible that the same
sampling unit may be drawn more than once. When the duplicate
number is ignored, the auditor is said to be sampling without
replacement.
Statistical tables used by auditors to determine sample size are
often based on sampling with replacement. As a practical matter,
however, the auditor usually samples without replacement
because no new information would be obtained from examining
the same item twice.
Systematic Sampling
Systematic sampling consists of selecting every nth item in the
population from one or more random starts. The interval
between items is usually referred to as the skip interval.
When a single random start is used, the interval can be calculated
by dividing the population size by the sample size.
A major advantage of systematic selection is that it may take less
time than other selection methods.
SAMPLING DALAM
PENGUJIAN SUBSTANTIF
Konsep Dasar
Sampling plans for substantive tests may be designed to:
1. Obtain evidence that an account balance is not materially
misstated or
2. Make an independent estimate of some amount.
Risiko Sampling
Audit sampling in substantive tests is subject to both sampling
risk and nonsampling risk. The sampling risks associated with
substantive tests are:
1. Risk of incorrect acceptance (beta risk) — the risk that the
sample supports the conclusion
that the recorded account
balance is not materially misstated when it is materially
misstated.
2. Risk of incorrect rejection (alpha risk) — the risk that the
sample supports the conclusion that the recorded account
balance is materially misstated when it is not materially
misstated.
Pendekatan Sampling
The following 2 statistical sampling approaches may be used by
the auditor in substantive tests:
1. Probability-proportional-to -size (PPS) sampling and
2. Classical variables sampling.
Pendekatan Sampling
Sampling Application Circumstances
AVAILABILITY OF INFORMATION
Book values for sampling units not available
Number of units in population unknown at start of sampling
Variability of population unknown
Appropriate
Sampling
Approach
Classical
PPS
Variables
X
X
X
CHARACTERISTICS OF POPULATION UNITS
Existence of zero or credit balances
EXPECTATIONS REGARDING MISSTATEMENTS
Expect no misstatements or only a few overstatements
Expect many misstatements or both under- and overstatements
X
X
X
Probability-Proportional-to-Size Sampling
PPS sampling is an approach that uses attribute sampling theory
to express a conclusion in dollar amounts rather than as a rate of
deviations. This form of sampling may be used in substantive
tests of both transactions and balances.
Probability-Proportional-to-Size Sampling
The steps in a PPS sampling plan are similar to those used in
attribute sampling. The steps are:
1. Determine the objectives of the plan
2. Define the population and sampling unit
3. Determine the sample size
4. Determine the sample selection method
5. Execute the sampling plan
6. Evaluate the sample results
Reliability Factors
RELIABILITY FACTORS FOR ZERO OVERSTATEMENTS
Reliability
Factor
1%
5%
Risk of Incorrect Acceptance
10%
15%
20%
25%
30%
4.61
3.00
2.31
1.90
1.61
1.39
1.21
37%
50%
1.00
0.70
Expansion Factors
EXPANSION FACTORS FOR ANTICIPATED MISSTATEMENTS
Expansion
Factor
1%
5%
Risk of Incorrect Acceptance
10%
15%
20%
25%
30%
1.90
1.60
1.50
1.40
1.30
1.25
1.20
37%
50%
1.15
1.00