In this study, the authors develop an inexpensive method to help firms assess the relative effectiveness of multiple advertising media. Specifically, they use a firm s loyalty program database to capture media exposure, through an online media survey, for all the media in which the firm advertises. In turn, the exposure data are matched with the purchase history for these same respondents, thereby creating single-source data. The authors illustrate their method for a large retailer that undertook a short-term promotional sale by advertising in television, radio, newspaper, magazine, online display ad, sponsored search, social media, catalog, direct mail, and e-mail channels. In this case, seven of the ten media significantly influence purchase outcomes. Finally, the authors demonstrate how to use their advertising response model to determine the optimal budget allocation across each advertising media channel.