Subject knowledge improves interactive query expansion assisted by a thesaurus

This study explores how experts and novices in pedagogics expanded queries supported by the ERIC thesaurus, and how this was connected to the search effectiveness in an easy and a difficult search task. The expert group consisted of 15 undergraduates in pedagogy and the novice group of 15 students with no previous studies in this field. Their search logs were recorded and a pre‐ and post‐search interview was conducted. The results show that the number and type of terms selected from the thesaurus for expansion by experts improved search effectiveness, whereas there were no connections between the use of thesaurus and improvement of effectiveness among novices. The effectiveness of expansions varied between the facets of the queries. Thus, a vital condition for benefiting from a thesaurus in query expansion to improve search results is sufficient familiarity with the search topic. The results suggest also that it is not in the first place the number of terms used in expansion, but their type and quality that are crucial for search success.