When auditing within the expenditure/disbursement cycle, auditors often rely predominantly on interim tests of controls rather than year end substantive tests of details.

In fact, in many cases, year end procedures consist primarily of updating the auditor's understanding of the system, testing payroll activities, and performing analytical procedures to test the reasonableness of reported payroll balances.

Required: 

Explain why an auditor might rely predominantly on tests of controls, rather than substantive tests of details in auditing payroll.