Out of sight, not out of mind

The information needs of users and the documents which answer it are frequently contingent on the different characteristics of users. This is especially evident during natural disasters, such as earthquakes and violent weather incidents, which create a strong transient information need. In this paper we investigate how the information need of users is affected by their physical detachment, as estimated by their physical location in relation to that of the event, and by their social detachment, as quantified by the number of their acquaintances who may be affected by the event. Drawing on large-scale data from three major events, we show that social and physical detachment levels of users are a major influence on their information needs, as manifested by their search engine queries. We demonstrate how knowing social and physical detachment levels can assist in improving retrieval for two applications: identifying search queries related to events and ranking results in response to event-related queries. We find that the average precision in identifying relevant search queries improves by approximately 18%, and that the average precision of ranking that uses detachment information improves by 10%.