The history of consumer marketing during the past two decades reflects a growing realization that information about customers is a key competitive asset. Airlines have spearheaded the development of loyalty programs, which offer valuable incentives to airline passengers in return for the ability to capture much more detailed profiles of frequent flyers. Banks have invested heavily to integrate information systems that facilitate access to broad activity profiles of customers across the major product categories offered by a bank. Credit information bureaus have compiled detailed credit histories of individual consumers. And retailers have developed point-of-sale information to track product movements and improve merchandising and promotion programs.

Yet much of the information marketers want most about consumers has nearly always been out of reach. When is a consumer going to make a purchase? What is the precise impact of advertising on that decision? What (and how much) are consumers buying from competitors and across categories?

What marketers really want is "demonstrated preference" information to show when a consumer is about to purchase

Online markets (e.g., the World Wide Web or proprietary online services such as America Online or CompuServe) hold the potential to allow consumer marketers to answer these questions for...