Which of the following is generally the least effective methodology to detect sales or accounts receivable skimming?

1. Count and summarize accounts receivable write-offs by employee.

2. Periodically review the back-up documentation, including approval for accounts receivable write-offs.

3. Examine accounts receivable transaction activity after regular business hours and at unusual times of the day and night.

4. Review the accounts receivable employee personnel records for prior terminations for fraudulent activity.