Analysis of change in users' assessment of search results over time.

We present the first systematic study of the influence of time on user judgements for rankings and relevance grades of web search engine results. The goal of this study is to evaluate the change in user assessment of search results and explore how users' judgements change. To this end, we conducted a large-scale user study with 86 participants who evaluated 2 different queries and 4 diverse result sets twice with an interval of 2 months. To analyze the results we investigate whether 2 types of patterns of user behavior from the theory of categorical thinking hold for the case of evaluation of search results: a coarseness and b locality. To quantify these patterns we devised 2 new measures of change in user judgements and distinguish between local when users swap between close ranks and relevance values and nonlocal changes. Two types of judgements were considered in this study: a relevance on a 4-point scale, and b ranking on a 10-point scale without ties. We found that users tend to change their judgements of the results over time in about 50% of cases for relevance and in 85% of cases for ranking. However, the majority of these changes were local.