In a field setting, you may not be able to manipulate the physical environment. Instead, you control the presentation and timing of the stimulus. You want to know whether sales people respond differently to customers of different races. You plan to have African American, Asian, and Caucasian students enter stores as "customers" in a local mall.

Each will enter alone and, using a stopwatch tucked into a pocket, will calculate the amount of time it takes for the sales person to approach. Using a stopwatch insures greater accuracy of the DV. If the sales person has not approached after 3 minutes, the student will leave the store. The student "customer" will also rate the level of help offered (0-none; 1- question; 2-show merchandise; 3-very involved).

Pilot tests will be conducted with "customers" in pairs to insure reliability of ratings. You choose only small stores because you want the sales staff to see the customer as soon as he or she enters the store; in large department stores, sales staff may not be physically present or may be occupied with many other customers. By limiting your study to small stores, you have controlled a source of variability.