Aggregated search interfaces provide users with an overview of results from various sources. Two general types of display exist: tabbed, with access to each source in a separate tab, and blended, which combines multiple sources into a single result page. Multi-session search tasks, e.g., a research project, consist of multiple stages, each with its own sub-tasks. Several factors involved in multi-session search tasks have been found to influence user search behavior. We investigate whether user preference for source presentation changes during a multi-session search task.   The dynamic nature of multi-session search tasks makes the design of a controlled experiment a non-trivial challenge. We adopt a methodology based on triangulation and conduct two types of observational study: a longitudinal study and a laboratory study. In the longitudinal study we follow the use of tabbed and blended displays by 25 students during a project.   We find that while a tabbed display is used more than a blended display, subjects repeatedly switch between displays during the project. Use of the tabbed display is motivated by a need to zoom in on a specific source, while the blended display is used to explore available material across sources whenever the information need changes.   In a laboratory study 44 students completed a multi-session search task composed of three sub-tasks, the first with a tabbed display, the second and third with blended displays. The tasks were manipulated by either providing three task about the same topic or about three different topics. We find that a stable information need over multiple sub-tasks negatively influences perceived usability of the blended displays, while we do not find an influence when the information need changes.
['Marc Bron', 'Jasmijn Van Gorp', 'Frank Nack', 'Lotte Belice Baltussen', 'Maarten de Rijke']
Aggregated search interface preferences in multi-session search tasks