The Dark Side of Relevance: The Effect of Non-Relevant Results on Search Behavior

ABSTRACT Understanding and modelling user behavior with search results is important to both search engine designers and the design of effectiveness measures. It is well established that users are less likely to view lower ranked search results, and recent research has shown that the type of relevant documents can influence when people stop examining results. However, while existing measures and research consider that relevant documents vary in utility and make use of relevance grades or preference judgments, non-relevant documents are largely all treated the same. In this paper, we show that the nature of non-relevant material affects users’ willingness to further explore a ranked list of search results. We first broaden our notion of non-relevant documents and define a spectrum of possible search engine result pages (SERPs). At one end of the spectrum, the search results were filled with off-topic non-relevant documents, and at the other end, the non-relevant documents were all on-topic, but failed to match the required sub-topic of the search task. We conducted a user study where participants used a mobile search interface to find answers to questions, and collected participants’ behavior while interacting with different SERPs on our spectrum. Our results show that user examination of search results, and time to query abandonment, is influenced by the coherence and type of non-relevant documents included in the SERP. When the SERP is coherent on an egregious topic, users spend the least amount of time before abandoning and are less likely to request to view more results. The time they spend increases as the SERP quality improves, and users are more likely to request to view more results when the SERP contains diversified non-relevant results on multiple subtopics. Our research implies that to improve information retrieval evaluation, we should be assessing the degree of non-relevance in search results as well as the degree of relevance.