This CISA practice question tests your understanding of information system auditing process. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which of the following is the most important factor to consider when determining sample size for a compliance test?
Tolerable error rate
Tolerable error rate is the primary driver; lower rates require larger samples.
Expected error rate
Why wrong: Expected error rate affects sample size but is not the most important factor.
Population size
Why wrong: Population size has a small impact on sample size for large populations.
Sampling method
Why wrong: Sampling method affects selection but not the fundamental sample size determination.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Tolerable error rate
In compliance testing (attribute sampling), the tolerable error rate is the maximum deviation rate from a control that the auditor is willing to accept without concluding the control is ineffective. It directly determines the required sample size because a lower tolerable error rate demands a larger sample to achieve sufficient precision, while a higher rate allows a smaller sample. This factor is more critical than others because it sets the boundary for the auditor's risk assessment.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Tolerable error rate
Why this is correct
Tolerable error rate is the primary driver; lower rates require larger samples.
Related concept
Read the scenario before looking for a memorised answer.
Expected error rate
Why it's wrong here
Expected error rate affects sample size but is not the most important factor.
Population size
Why it's wrong here
Population size has a small impact on sample size for large populations.
Sampling method
Why it's wrong here
Sampling method affects selection but not the fundamental sample size determination.
Common exam traps
The trap here is that candidates often confuse 'expected error rate' (a planning estimate) with 'tolerable error rate' (the maximum acceptable deviation), mistakenly thinking the expected rate is more important because it seems to reflect reality, but the tolerable rate is the key risk-based parameter that governs sample size.
Detailed technical explanation
Under the hood, sample size for compliance tests is derived from the binomial distribution using the formula n = (Z² × p × (1-p)) / E², where Z is the z-score for the desired confidence level, p is the expected error rate, and E is the tolerable error rate. In practice, auditors use tables or software (e.g., IDEA, ACL) that incorporate these parameters, and the tolerable error rate is the primary driver because it directly reflects the auditor's materiality threshold for control risk. A real-world scenario: if a control's tolerable error rate is set at 2% versus 5%, the sample size can increase by over 300% for the same confidence level, highlighting its dominant role.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the CISA exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
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FAQ
Information System Auditing Process — This question tests Information System Auditing Process — Read the scenario before looking for a memorised answer..
The correct answer is: Tolerable error rate — In compliance testing (attribute sampling), the tolerable error rate is the maximum deviation rate from a control that the auditor is willing to accept without concluding the control is ineffective. It directly determines the required sample size because a lower tolerable error rate demands a larger sample to achieve sufficient precision, while a higher rate allows a smaller sample. This factor is more critical than others because it sets the boundary for the auditor's risk assessment.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
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