During the course of an audit some of the following evidence is obtained by the auditor:

1. creditor’s monthly statement from the entity’s files;

2. management working papers in making accounting estimates;

3. letter from a customer stating that she will pay a balance owing;

4. bank statement confirmation sent directly to the auditor;

5. duplicate sales invoices filed in the entity’s office;

6. bank statement from the entity’s files;

7. material requisitions filed in the storeroom;

8. memo from the financial accountant authorising payment of an account for new equipment.

Required

(a) Classify the evidence by source into one of four categories: (1) directly from outsiders, (2) indirectly from outsiders, (3) internal but validated externally, and (4) entirely internal.

(b) Comment on the reliability of the four sources of documentary evidence.