Ximena wants to measure the effects of amount of body spray on perceived attractiveness. She divides her research assistants into groups and applies no body spray, a small amount of body spray, or a large amount of body spray to each group. Ximena then asks passersby on campus to rate the attractiveness of each participant on a scale of 1 to 5 following a three-minute interaction. In this example, the variable amount of body spray has levels, and the variable of attractiveness has levels