Indicate which of the following audit procedures, used as tests of controls, do not involve audit sampling.

1. Observing and evaluating segregation of duties.

2. Testing of whether sales invoices are supported by authorized customer orders and shipping documents.

3. Reviewing entity's procedures for accounting for the numerical sequence of shipping documents.

4. Examining sales orders for proper credit approval.

5. Recomputing the information on copies of sales invoices.

6. Comparing the average days outstanding in accounts receivable with industry averages.