Starting with a discussion of two analyses from a recently published multibrand study, this paper argues that such work could help us learn much more about the effects of different marketing and planning decisions. The paper outlines a proposal which develops this idea. It proposes a major programme of further analyses of the existing databases in the hands of the major syndicated research services such as purchase panels, shop audits and ad awareness studies. Key aspects and benefits of the proposal are identified. A high level of cooperative effort would be required, involving advertisers, advertising agencies and the research companies. Media owners would also want to be closely involved, but in a different manner because they are not directly involved in the purchase and interpretation of the data to be used. We are on the threshold of being able to build a much improved starter kit of market planning knowledge, with the potential for delivering a greatly improved marketing ROI. The question is no longer how to improve marketing efficiency, but when?