The article presents results of a study on search behavior in an interactive query expansion environment. In controlled experiments, users’ search behavior in retrieval system versions with varying levels of query expansion support is compared. On the one hand, the analysis of query logfiles reveals that interactive expansion term suggestions encourage users to utilize a wider variety of term tactics for reformulating their queries than users of a baseline group who are not offered any query expansion support. On the other hand, the experimental results indicate that the interactive expansion functionalities foster the application of facet expansion tactics in favor of the replacement tactic which prevails in system versions that do not offer interactive query expansion support. In summary, the study gives evidence that the implementation of interactive expansion term suggestions adds both to the complexity of the users’ queries and to the variety of their query vocabulary.
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