Predicting search task difficulty at different search stages

Knowing, in real time, whether a current searcher in an information retrieval system finds the search task difficult can be valuable for tailoring the system's support for that searcher. This study investigated searcher's behaviors at different stages of the search process; they are: 1) first-round point at the beginning of the search, right before searchers issued their second query; 2) middle point, when searchers proceeded to the middle of the search process, and 3) end point, when searchers finished the whole task. We compared how the behavioral features calculated at these three points were different between difficult and easy search tasks, and identified behavioral features during search sessions that can be used in real-time to predict perceived task difficulty. In addition, we compared the prediction performance at different stages of search process. Our results show that a number of user behavioral measures at all three points differed between easy and difficult tasks. Query interval time, dwell time on viewed documents, and number of viewed documents per query were important predictors of task difficulty. The results also indicate that it is possible to make relatively accurate prediction of task difficulty at the first query round of a search. Our findings can help search systems predict task difficulty which is necessary in personalizing support for the individual searcher.