Estimating query difficulty for news prediction retrieval

News prediction retrieval has recently emerged as the task of retrieving predictions related to a given news story (or a query). Predictions are defined as sentences containing time references to future events. Such future-related information is crucially important for understanding the temporal development of news stories, as well as strategies planning and risk management. The aforementioned work has been shown to retrieve a significant number of relevant predictions. However, only a certain news topics achieve good retrieval effectiveness. In this paper, we study how to determine the difficulty in retrieving predictions for a given news story. More precisely, we address the query difficulty estimation problem for news prediction retrieval. We propose different entity-based predictors used for classifying queries into two classes, namely, Easy and Difficult. Our prediction model is based on a machine learning approach. Through experiments on real-world data, we show that our proposed approach can predict query difficulty with high accuracy.