The primary focus of this dissertation is to answer the question: how does exposure to advertising affect purchasing behavior, and in particular, how does synergy resulting from exposure to advertising in multiple media influence purchasing behavior? This is a critical piece of information in the business decision process of media planning. It determines which media to include in a media plan and how to allocate a limited budget across media in order to optimize the return on investment from advertising. This question has been studied in many ways since it has been a central question for the advertising industry for over forty years. Researchers have: (1) examined the question using one medium, (2) built models in the hopes that data would be collected to test them, (3) used surrogate measures for exposure, such as commercial recall, (4) used exposure rather than response (sales) as a measure, and (5) used surrogate measures for sales, such as brand preference or intent to buy. This dissertation uses the data from Project Apollo, a single source database of passive (or electronically captured) longitudinal measurements of advertising exposure and household level consumer packaged goods sales, to answer this question. The limitations of this approach are that the tools to analyze single source data are still in their infancy, the media that have been included are only magazines and television, and the products examined are fast moving consumer package goods (FMCG) categories.