In Simple Terms:
Audit sampling means testing a carefully selected portion of a larger population to obtain audit evidence about the population as a whole.
What Is Audit Sampling?
Audit sampling is an audit procedure in which the auditor applies testing procedures to fewer than 100% of the items in a relevant population and uses the results to draw conclusions about that population.
The objective is not simply to test fewer items. The sample should be designed and selected to provide an appropriate basis for the auditor’s conclusion. This requires a clearly defined audit objective, an appropriate population, a defensible selection method, an adequate sample size, appropriate testing procedures, and documented evaluation of the results.
In practice, audit sampling allows auditors to obtain audit evidence from a representative or appropriately selected portion of a population without examining every item. The results are then evaluated to determine whether they support the audit objective and whether exceptions or deviations require further investigation.
Why Is Audit Sampling Used in Auditing?
1. Makes Testing Practical
A large population may make 100% testing impractical. Sampling allows auditors to focus testing on a manageable number of items.
2. Obtains Audit Evidence
A properly designed sample can provide evidence that supports conclusions about a population.
3. Improves Efficiency
Reduces unnecessary testing while allowing auditors to focus resources on areas that matter most.
4. Supports Risk-Based Auditing
Sampling decisions should be connected to the audit objective, risk assessment, and overall audit plan.
5. Tests Recurring Controls
Determine whether controls operated consistently during a defined period.
Key Terms Used in Audit Sampling
Types of Audit Sampling
Statistical Audit Sampling
Uses probability theory to select samples and evaluate results. Characteristics include random selection, defined sampling parameters, quantifiable sampling risk, structured sample-size determination, and statistical evaluation of results.
Non-Statistical Audit Sampling
Relies more heavily on professional judgment. The auditor determines the sample based on factors such as audit objective, risk, materiality, population characteristics, expected exceptions, and previous audit results.
Note:
SA 530 recognizes both statistical and non-statistical approaches to audit sampling. Non-statistical sampling is not automatically inferior to statistical sampling.
Audit Sampling Methods
Random Sampling
Items selected using a random mechanism. Best suited for large transaction populations and general control testing.
Systematic Sampling
Selects items using a defined interval after establishing an appropriate starting point.
Monetary Unit Sampling
Gives greater selection weight to monetary values. Useful when the audit objective is focused on potential overstatement.
Haphazard Sampling
Selecting items without formal randomization while attempting to avoid conscious bias.
Block Sampling
Selecting a contiguous group of items. Use with caution as a single block may not represent the entire population.
Judgmental/Targeted Selection
Deliberately selecting items with particular risk characteristics: high-value, unusual, previous exceptions, privileged users.
Audit Sampling Techniques
- Random selection: Each sampling unit has a defined chance of selection
- Stratification: Dividing population into groups (high/medium/low value, business unit, geography)
- High-value item testing: Large or individually significant items tested separately
- Risk-based selection: Items with higher risk receive greater attention
- Exception-focused testing: Investigating unusual items or previous exceptions
- Combined approaches: High-value items tested separately, remaining population subjected to systematic sampling
How to Determine Audit Sample Size
One of the most common mistakes in audit sampling is treating sample size as a fixed percentage of the population. There is no universal rule that makes 10% an appropriate sample for every audit. Sample size should be determined based on the audit objective, assessed risk, tolerable deviation or misstatement, expected deviation or misstatement, and the level of assurance required—not simply as a fixed percentage of the population.
Factors That Influence Sample Size
- Population size: Number of items in the population
- Risk: Higher assessed risk may require more extensive testing
- Tolerable deviation or misstatement: The amount of error the auditor is willing to accept
- Expected deviation or misstatement: The rate of deviations the auditor expects
- Desired assurance: Level of assurance from the sampling procedure
- Population characteristics: Whether stratification or other approaches are needed
Example
Suppose an internal auditor needs to test 15,000 purchase transactions. Instead of choosing 1,500 because it represents 10%, the auditor should consider:
- What exactly is the population?
- What is the sampling unit?
- What control is being tested?
- What is the assessed risk?
- What deviation rate is acceptable?
- What deviation rate is expected?
- What level of assurance is required?
- Which sampling approach is appropriate?
- Are high-value or high-risk transactions being tested separately?
Audit Sampling Risk
Sampling risk is the possibility that the conclusion reached from testing a sample differs from the conclusion that would have been reached if the entire population had been tested.
Risk of Incorrect Acceptance
Concluding that a population is acceptable when it is not. Can result in insufficient audit response to a problem.
Risk of Incorrect Rejection
Concluding that a population is not acceptable when the true population condition would support an acceptable conclusion.
Audit Sampling for Tests of Controls
Sampling is commonly used to test whether a control operated consistently over a period.
Example
An organization requires all purchase orders above ₹1 lakh to receive approval from an authorized manager. The auditor may:
- Define the population of relevant purchase orders
- Establish the audit objective
- Determine the sampling approach
- Select the sample
- Verify the required approval for each selected transaction
- Record deviations
- Evaluate the results
- Document the conclusion
What is a Control Deviation?
A deviation occurs when the prescribed control was not performed as required. For example, a purchase order exists but the required approval is missing. That item represents a control deviation that should be evaluated.
Audit Sampling for Tests of Details
Tests of details examine individual transactions, balances, or supporting information. Examples include testing invoice amounts, account balances, purchase transactions, sales transactions, supporting documents, vendor balances, expense claims, and journal entries.
Important:
Audit sampling is not itself a test of details. Sampling is a method for selecting items for testing. The selected items may then be subjected to tests of details, tests of controls, or other appropriate audit procedures depending on the audit objective.
Audit Sampling vs 100% Testing
Audit Sampling Examples
Example 1: Purchase Transactions
An organization has 20,000 purchase transactions. The auditor defines the population, identifies the sampling unit, determines the sampling approach, selects the sample, checks purchase orders and invoices, verifies approval, records exceptions, evaluates results, and documents the conclusion.
Example 2: User Access Review
An organization has 3,500 active user accounts. The auditor tests selected users for access request, manager approval, role assignment, privileged access, employment status, termination status, and periodic access review. High-risk privileged accounts may be subject to separate targeted testing.
Example 3: Vendor Compliance
An organization has 1,000 vendors. The auditor examines vendor onboarding records, contracts, risk assessments, security assessments, compliance certificates, approvals, and periodic reviews.
How to Do Audit Sampling in Excel
Step 1: Prepare the Population
Create a complete list of items available for selection.
Step 2: Assign a Unique Identifier
Every sampling unit should have a unique identifier (e.g., TX001, TX002).
Step 3: Add a Random Number
Use Excel’s =RAND() function to generate random values for sorting or selection.
Step 4: Record the Selected Sample
Maintain a separate record of population, sample size, selection methodology, selected items, testing status, exceptions, reviewer comments, and final conclusion.
Step 5: Preserve the Sampling Evidence
Do not rely only on a temporary Excel filter. The audit file should retain enough information to explain how and why the sample was selected.
Audit Sampling Documentation
An audit workpaper should generally make it possible for another reviewer to understand:
- Audit objective
- Population
- Sampling unit
- Sampling method
- Sample size and rationale
- Risk considerations
- Testing procedure
- Exceptions
- Evaluation
- Conclusion
Audit Sampling vs Audit Evidence
Sampling determines which items are tested. Audit evidence is the information obtained and evaluated during the audit. A sampling approach should be designed around the evidence required to address the audit objective.
Audit Sampling vs Data Analytics
Data analytics can sometimes support population-level testing or identify unusual transactions that warrant targeted audit procedures.
Audit Sampling Best Practices
Common Audit Sampling Mistakes
Audit Sampling Software and Tools
Audit sampling software can help auditors define audit populations, select samples, apply sampling methodologies, record selected items, document testing, record exceptions, maintain review history, link evidence to testing, and track audit conclusions.
Audit Sampling Workflow
Audit Sampling Checklist
Frequently Asked Questions
Final Takeaway
Audit sampling is not simply about deciding how many transactions to test. A defensible sampling process starts with the audit objective and moves through the population, risk, materiality, sampling approach, sample selection, testing, evaluation, and documentation.
The strongest sampling methodology answers five questions:
- What are we trying to determine?
- What population are we testing?
- Why did we select this sample?
- What did the testing show?
- What does the result mean for the population?
For organizations managing recurring audits, sampling becomes easier to govern when the population, selected items, evidence, exceptions, findings, and corrective actions remain connected throughout the audit lifecycle.
Ready to Streamline Your Audit Sampling Process?
Connect sampling with the broader audit lifecycle so that sample selection, evidence, exceptions, findings, and corrective actions remain traceable in one system.
