On the impact of group size on collaborative search effectiveness

Felipe Moraes, Kilian Grashoff, Claudia Hauff*

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

5 Citations (Scopus)


While today’s web search engines are designed for single-user search, over the years research efforts have shown that complex information needs—which are explorative, open-ended and multi-faceted—can be answered more efficiently and effectively when searching in collaboration. Collaborative search (and sensemaking) research has investigated techniques, algorithms and interface affordances to gain insights and improve the collaborative search process. It is not hard to imagine that the size of the group collaborating on a search task significantly influences the group’s behaviour and search effectiveness. However, a common denominator across almost all existing studies is a fixed group size—usually either pairs, triads or in a few cases four users collaborating. Investigations into larger group sizes and the impact of group size dynamics on users’ behaviour and search metrics have so far rarely been considered—and when, then only in a simulation setup. In this work, we investigate in a large-scale user experiment to what extent those simulation results carry over to the real world. To this end, we extended our collaborative search framework SearchX with algorithmic mediation features and ran a large-scale experiment with more than 300 crowd-workers. We consider the collaboration group size as a dependent variable, and investigate collaborations between groups of up to six people. We find that most prior simulation-based results on the impact of collaboration group size on behaviour and search effectiveness cannot be reproduced in our user experiment.

Original languageEnglish
Pages (from-to)476–498
Number of pages23
JournalInformation Retrieval Journal
Issue number5
Publication statusPublished - 2019


  • Collaborative search
  • Interactive search
  • Search effectiveness


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