Sufficiency - Sources of evidence
The audit evidence should in total enable the auditor to form an opinion on the financial statements. Sufficiency is a measure of evidence obtained of the quantity. How much evidence to obtain, what source to use, and the form the evidence should take is an issue left to the auditor to exercise his judgment in the light of the opinion called for under the terms of his engagement. Of crucial importance however, he will be influenced by the materiality of the matter to be examined, the reliability and relevance of evidence available from each source and the cost and time involved in obtaining it.
Quite frequently when the auditor obtains evidence from some sources that put when together gives him the necessary assurance. Factors that affect sufficiency are usually dictated by the degree of risk of misstatement. The risk itself is affected by the nature of the item, the adequacy of internal control, the nature of the business carried on by the entity, situations which may exact an unusual influence on management, the financial position of the entity, the materiality of the item in relation to the financial statements taken as a whole, the auditor's experience as to the reliability of the management staff of the enterprise and its records, the results of auditing procedures including fraud or error which may have been found and the type of information available.