The auditor needs to obtain the same level of assurance in order to express an unqualified opinion on the financial statements of both small and large entities. However, many internal controls which would be
relevant to large entities are not practical in the small business. For example, in small businesses, accounting procedures may be performed a few persons who may have both operating and custodial responsibilities, and therefore segregation of duties may be missing or severely limited. Inadequate segregation of duties may, in some cases, be offset a strong management control system in which owner/manager supervisory controls exist because of direct personal knowledge of the entity and involvement in transactions. In circumstances where segregation of duties is limited and audit evidence of supervisory controls is lacking, the audit evidence necessary to support the auditor‟s opinion on the financial statements may have to be obtained entirely through the performance of substantive procedures.