When Does Retargeting Work ? Timing Information Specificity ∗

Firms can now serve personalized recommendations to consumers who return to their website, based on their earlier browsing history. At the same time, online advertising has greatly advanced in its use of external browsing data across the web to target internet ads appropriately. ‘Dynamic Retargeting’ integrates these two advances by using information from internal browsing data to improve internet advertising on external websites. Consumers who previously visited the firms’ website are shown ads that reflect the specific products they have looked at before on the firm’s own website when surfing the wider web. To examine whether this is more effective than simply showing generic brand ads, we use data from a field experiment conducted by an online travel firm. We find, surprisingly, that increased ad specificity is on average less effective than generic information. We provide evidence that this can be explained by a mismatch between the specificity of this form of advertising and whether a consumer has well-defined product preferences. Only when consumers have well-defined product preferences and are actively engaged in the category are specific ads more effective than generic ads. ∗We thank Havas Digital and particularly Katrin Ribant for access to data from Artemis and Marco Bertini for facilitating the contact to Havas Digital. We gratefully acknowledge financial support from the London Business School Centre for Marketing. We thank participants at the 2011 SICS conference and seminar participants at Cass Business School, ESMT, ESSEC, London Business School and the National University of Singapore for useful comments. †London Business School, London, UK; [email protected]. ‡MIT Sloan School of Management, MIT, Cambridge, MA; [email protected] and NBER