Queries on major Web search engines produce complex result pages, primarily composed of two types of information: organic results, that is, short descriptions and links to relevant Web pages, and sponsored search results, the small textual advertisements often displayed above or to the right of the organic results.  Strategies for optimizing each type of result in isolation and the consequent user reaction have been extensively studied; however, the interplay between these two complementary sources of information has been ignored, a situation we aim to change.  Our findings indicate that their perceived relative usefulness (as evidenced by user clicks) depends on the nature of the query. Specifically, we found that, when both sources focus on the same intent, for navigational queries there is a clear competition between ads and organic results, while for non-navigational queries this competition turns into synergy.

We also investigate the relationship between the perceived usefulness of the ads and their textual similarity to the organic results, and propose a model that formalizes this relationship. To this end, we introduce the notion of responsive ads, which directly address the user's information need, and incidental ads, which are only tangentially  related to that need. Our findings support the hypothesis that in the case of navigational queries, which are usually fully satisfied by the top organic result, incidental ads are perceived as more valuable than responsive ads, which are likely to be duplicative. On the other hand, in the case of non-navigational queries, incidental ads are perceived as less beneficial, possibly because they diverge too far from the actual user need.

We hope that our findings and further research in this area will allow search engines to tune ad selection for an increased synergy between organic and sponsored results, leading to both higher  user satisfaction and better monetization.