Advanced Auditing, Assurance and Professional Ethics · Audit Evidence

Reliability of Audit Evidence and Information Used (SA 500)

Updated 5 October 2026 · Fact-checked

Reliability is the degree to which audit evidence can be trusted. Under SA 500 it depends on the source, nature and circumstances of the evidence. For information used as evidence, you must also test its accuracy and completeness. To solve a question, name the source, apply the generalisations, then conclude on what more work is needed.

Understand Reliability of Audit Evidence and Information Used

Audit evidence has two qualities: sufficiency (how much) and appropriateness (how good). Appropriateness has two parts: relevance and reliability. This page is about reliability. Evidence you cannot trust does not become useful just because you have a lot of it.

SA 500 says reliability depends on the source and nature of the evidence, and on the circumstances in which it is obtained. Source means who produced it: inside the entity (internal) or outside it (external). Nature means its form: documentary, written, electronic, or oral. Circumstances include the controls over its preparation and maintenance.

From this SA 500 gives generalisations. These are rules of thumb, not laws. Each is true only if the stated condition holds, and you should say so in your answer.

There is a second layer. Often the auditor uses information produced by the entity, such as an ageing report, a stock listing or a system-generated report, as the base for a procedure. SA 500 requires you to evaluate whether that information is sufficiently reliable for your purpose. This means obtaining evidence about its accuracy (is each item recorded correctly?) and completeness (are all items included?), and evaluating whether it is precise and detailed enough for your purpose.

If evidence from one source is inconsistent with evidence from another, or you doubt the reliability of information, you must determine what changes or additional procedures are needed, and consider the effect on other aspects of the audit.

Key rules to remember

Appropriateness of audit evidence: Appropriateness = Relevance + Reliability; It is a measure of the quality of evidence. Relevance means it bears on the assertion tested; reliability means it can be depended on.
Factors of reliability: Reliability depends on: source + nature + circumstances; Use these three words as headings in every answer.
Generalisation 1: external source: External sources (independent of the entity) are more reliable than internal sources; Holds when the external source is independent and knowledgeable. Not if it is a related party or lacks competence.
Generalisation 2: effective controls: Evidence generated internally is more reliable when the related controls, including those over its preparation and maintenance, are effective; If controls are weak, internal evidence loses reliability.
Generalisation 3: direct knowledge: Evidence obtained directly by the auditor is more reliable than evidence obtained indirectly or by inference; Example: observing a control is more reliable than inquiring about it.
Generalisation 4: documentary form: Evidence in documentary form (paper, electronic or other) is more reliable than evidence obtained orally; A written record made at the time of events is more reliable than later oral recollection.
Generalisation 5: originals: Original documents are more reliable than photocopies, facsimiles, or documents that are filmed, digitised or otherwise transformed into electronic form; The reliability of the transformed document may depend on the controls over its preparation and maintenance.
Information used as evidence: Information produced by the entity: test accuracy + completeness; evaluate whether precise and detailed enough for the purpose; Applies before you rely on a report to select a sample, run a test or form an expectation.

How to solve Reliability of Audit Evidence and Information Used questions

Use this method for any case scenario or written question on reliability. It keeps your answer in provision, facts, conclusion form.

1Identify the assertion and the evidence in the case. Write what the auditor has obtained and why.
2Classify the source: internal or external. Check whether an external source is truly independent and competent.
3Classify the nature: documentary or oral; original or copy; direct or indirect.
4Check the circumstances: are controls over the preparation and maintenance of the evidence effective? Note any IT or manual-override issues.
5Apply the relevant SA 500 generalisation and state its condition. Do not say 'always'.
6If the entity's own report or data is used, say what you will do to test its accuracy and completeness, and whether it is precise and detailed enough.
7Conclude: reliable enough or not. If not, or if sources conflict, state the additional procedures needed and the effect on other aspects of the audit.

Quickest way: S-N-C-A-C check

When to use it: When you have under five minutes for a case-scenario MCQ or a short written answer.

S: Source. Internal or external?
N: Nature. Documentary or oral, original or copy, direct or indirect?
C: Circumstances. Are the controls effective?
A and C: Accuracy and completeness. If the entity's report is the base, how was each tested?
Pick the option that matches the generalisation, then check whether the case removes its condition, for example a related-party external source.

Common mistakes in Reliability of Audit Evidence and Information Used

Writing that external evidence is always more reliable.
Students memorise the generalisation without its condition.
Fix: Say 'generally more reliable, if independent and competent'. Check the case for related parties or doubtful competence.
Treating a system-generated report as reliable because it comes from software.
Automation looks objective.
Fix: State that you must test the accuracy and completeness of the report logic and data, and evaluate whether it is detailed enough for the purpose.
Confusing reliability with sufficiency.
Both sit under 'sufficient appropriate' and look similar.
Fix: Sufficiency is quantity. Reliability is a part of appropriateness, which is quality. More low-quality evidence does not fix poor reliability.
Ignoring the controls over internal evidence.
Students stop at 'internal is less reliable'.
Fix: Add that internal evidence gains reliability when related controls are effective, and link to your control testing.
Stopping after finding a reliability concern.
Answer ends with a label such as 'not reliable'.
Fix: Always state the response: additional procedures, and the effect on other aspects of the audit.
Ranking oral confirmation above a document because it is from a senior person.
Seniority is mistaken for evidence quality.
Fix: Oral evidence is generally less reliable. Seek corroboration, or written representations where appropriate.

Worked examples

Example 1

Case: While auditing trade receivables of Meru Traders Ltd, the auditor has two pieces of evidence for a ₹8,40,000 balance: (a) a balance confirmation received directly from the customer, an unrelated party, and (b) a copy of the sales invoice kept by the company's accounts team. Which is more reliable and why?

Show the solution

Assertion: existence of the receivable.
Source: (a) is external and independent of the entity; (b) is internal.
Nature and circumstances: (a) was received directly by the auditor, so it is direct evidence with no scope for management interference. (b) is a copy, and copies are generally less reliable than originals.
Apply the generalisations: external evidence is generally more reliable than internal evidence, and original documents more than copies.
Condition check: the customer is unrelated and its competence is not in doubt in the case.

Answer: The customer's confirmation is more reliable. It is external, independent and obtained directly. The invoice copy is internal and a copy. The auditor may still use the invoice as corroboration.

Example 2

Case: For testing inventory valuation, the auditor of Kaveri Foods Ltd selects 40 items from a stock ageing report generated by the company's ERP. The report is used to identify slow-moving stock. The auditor accepts the report as the entity's system produced it. Evaluate the approach.

Show the solution

The ageing report is information produced by the entity and used as the base for an audit procedure.
SA 500 requires the auditor to evaluate whether the information is sufficiently reliable for the purpose.
Accuracy: test whether items carry the correct dates and quantities, for example by agreeing a sample to goods receipt notes and by testing the ageing logic.
Completeness: test that all stock items are in the report, for example by agreeing the report total to the general ledger and tracing physical items to the report.
Precision: evaluate whether the ageing bands are detailed enough to identify slow-moving items for the purpose.
Because the report is internal, effective IT general controls would raise its reliability. If controls are weak, do more direct testing.
Conclusion: accepting the report without these tests is not appropriate.

Answer: The approach is not appropriate. The auditor must obtain evidence about the accuracy and completeness of the report and evaluate whether it is precise and detailed enough before using it. Only then can the sample from it support conclusions on valuation.

Exam tips

In case-scenario MCQs, look for the one fact that removes a generalisation's condition, such as a related-party confirmation or a weak control environment.
In written answers, use the headings Source, Nature, Circumstances. Then give accuracy and completeness if entity-produced information is used.
Write 'generally' or 'is more reliable if...' when stating generalisations. Never write 'always'.
End every answer with an action: additional procedures or corroboration. Marks are usually given for the conclusion.
Link to SA 500 sufficiency and appropriateness, and to SA 505 for external confirmations, in one sentence to show breadth.

Practice questions from Audit Evidence

Reliability of Audit Evidence and Information Used in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

CA IntermediateAudit Evidence: Meaning, Nature and SA 500

Reliability of Audit Evidence and Information Used: frequently asked questions

What decides the reliability of audit evidence under SA 500?

Its source, its nature and the circumstances in which it is obtained. These include the controls over its preparation and maintenance. SA 500 gives generalisations to help judge it, but each depends on its conditions.

Is external evidence always more reliable than internal evidence?

No. It is generally more reliable when the source is independent of the entity and competent. A related party or an incompetent source can weaken it. Internal evidence can also be reliable if controls over it are effective.

What must I do when I use a report from the entity's system as audit evidence?

Obtain evidence about the accuracy and completeness of the information. Also evaluate whether it is precise and detailed enough for your purpose. This applies when it is the base for a sample, an analytical procedure or any other test.

What if evidence from two sources conflicts?

Determine what changes or additional procedures are needed to resolve the matter. Consider the effect, if any, on other aspects of the audit. Do not rely on either source until you resolve the inconsistency.