A retailer of tapes and compact disks wants to test whether people can dif- ferentiate the two products by the quality of sound only. A random sample of con- sumers who agreed to participate in the test and who have no particular experience with high-quality audio equipment is selected. The same musical performance is played for each person, once on a disk and once on a tape. The listeners do not know which is playing, and the order has been determined randomly. Each person is asked to state which of the two performances he or she prefers. What statistical test is most appropriate here? Why?