general hospital is performing peer reviews of its medical providers for quality outcomes of care. the hospital has over 500 providers on its medical staff. the process to review even 10 cases for each provider is quite extensive. the quality department has concluded that, to accomplish this review process, it will review 20 percent of each provider's inpatient admissions to the hospital on an every-other-year rotation. in this situation, the quality department has applied which of the following techniques to its review process?