As shown in the table, the multi-parameter model improves by approximately 18% and 12% on the TREC-6 and 7 partial query sets, and it also significantly outperforms both the word model and the one-parameter model on the TREC-8 query set.
the improvement on the TREC-8 query set shows one advantage of using our proposed method; by separating potentiallyineffective phrases and effective phrases based on the features, it not only improves the retrieval performance for each query but makes parameter learning less sensitive to the training set.