David Ogilvy once said of direct marketers: "We sell, or else." Ogilvy was a very smart man. However, many of today's professionals still are not aware of how their marketing performs. They don't know if it sells or, if it does, they don't know why. This is why there is no substitute for evidence-based marketing. Evidence-based marketing can be defined as the combination of proven marketing methods with intensive and meticulous testing, all tied to the commitment of measuring the impact of each message in each medium.