document: Here , there , and everywhere : correlated online behaviors can lead to overestimates of the effects of advertising Measuring the causal effects of online advertising ( adfx ) on user behavior is important to the health of the WWW publishing industry . In this paper , using three controlled experiments , we show that observational data frequently lead to incorrect estimates of adfx . The reason , which we label `` activity bias , '' comes from the surprising amount of time-based correlation between the myriad activities that users undertake online . In Experiment 1 , users who are exposed to an ad on a given day are much more likely to engage in brand-relevant search queries as compared to their recent history for reasons that had nothing do with the advertisement . In Experiment 2 , we show that activity bias occurs for page views across diverse websites . In Experiment 3 , we track account sign-ups at a competitor 's ( of the advertiser ) website and find that many more people sign-up on the day they saw an advertisement than on other days , but that the true `` competitive effect '' was minimal . In all three experiments , exposure to a campaign signals doing `` more of everything '' in given period of time , making it difficult to find a suitable `` matched control '' using prior behavior . In such cases , the `` match '' is fundamentally different from the exposed group , and we show how and why observational methods lead to a massive overestimate of adfx in such circumstances .
doc_bio_tags: O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O