Audit evidence consists of the documents you use during an audit to substantiate your audit opinion. While working on an audit, you encounter many different types of evidence (written, oral, and so on). Documents can be prepared by employees of the client or by outside parties. To properly evaluate the strength of evidence you gather, you have to understand the four concepts of evidence:
Nature: The form of the evidence — for example, oral, visual, or written.
Appropriateness: The quality, relevancy, and reliability of the evidence.
Sufficiency: The quantity of audit evidence — enough evidence to evaluate the audit client’s management assertions.
Evaluation: A decision on whether the evidence is compelling enough to allow you to form an opinion.