NAPA Car Parts is a retail chain specializing in stocking and selling both domestic and foreign automobile parts. It is interested in learning about its customers, so the marketing director sends instructions to all 2000 store managers telling them that whenever a customer makes a purchase of $150 or more, they are to write down a description of the customer who made that purchase. They are to do this just for the second week in October, writing each description on a separate sheet of paper. At the end of the week, they are to send all sheets to the marketing director. Which data collection method is utilized in this example?