Audit Sampling Methods: Statistical vs Non-Statistical, Attributes vs Variables
Auditors cannot test every transaction. Instead, they use audit sampling to obtain sufficient appropriate audit evidence. Understanding the different methods is essential for effective auditing.
What is Audit Sampling?
Audit sampling is applying audit procedures to less than 100% of items to obtain audit evidence about a population.
Types of Sampling Methods
1. Statistical vs Non-Statistical
| Type | Description |
|---|---|
| Statistical | Random selection with quantifiable results; allows calculation of sampling risk |
| Non-statistical | Judgmental selection; auditor relies on experience |
2. Attributes vs Variables Sampling
| Type | Purpose | Example |
|---|---|---|
| Attributes | Test controls | Is invoice approved? Yes/No |
| Variables | Test monetary amounts | What is the value of inventory? |
Common Sampling Techniques
Haphazard Selection
Selecting items without bias but not using mathematical random selection.
Random Selection
Every item in the population has an equal chance of selection.
Systematic Selection
Selecting every nth item (e.g., every 10th item) after a random start.
Monetary Unit Sampling (MUS)
Each dollar is a sampling unit; higher value items have higher chance of selection.
Sample Size Determination
| Factor | Effect on Sample Size |
|---|---|
| Higher sampling risk | Increase |
| Larger tolerable deviation rate | Decrease |
| Higher expected deviation rate | Increase |
| More assurance from controls | Decrease |
ISA 530 Requirements
- Sample must be representative of population
- Select items with specific characteristics
- Document sampling methodology
- Evaluate results and draw conclusions
Key Takeaways
- Statistical sampling allows quantifiable conclusions
- Attributes sampling tests controls
- Variables sampling tests monetary amounts
- Sample size depends on risk and materiality
