This technical note is used in Darden's first-year core marketing course as well as in the marketing analytics elective. It could also be used effectively in modules covering the topics of market research, web analytics, or advertising. The note pairs well with the case "Advertising Experiments at the Ohio Art Company" (UVA-M-0752), which includes a student spreadsheet and a teaching note for instructors. Marketing managers must often face the challenge of justifying investment in a marketing mix, despite the difficulty of isolating the effect of any particular marketing activity. This note introduces experiments as a means of establishing causality and thus a campaign's projected efficacy.