During the course of an examination, the auditor examines a wide variety of documentation. Listed below are some forms of documentary evidence and the source from which they are obtained:

1. Bank statement obtained directly by the auditor from a bank 2. Creditor monthly statement obtained from client's files.

3. Vouchers in client's unpaid voucher file.

4. Duplicate sales invoices in filled order file.

5. Time tickets filed in payroll depariment.

6. Credit memo in customer's file.

7. Material requisitions filed in storeroom.

8. Bank statement in client's files.

9. Invoices from suppliers.

10. Paid checks returned with bank statement in 1 above.

\section*{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 evidence.