NTCIR-6 Chinese Monolingual and English-Chinese Cross Language Retrieval Experiments using PIRCS

In NTCIR-6, our Stage-1 results which consist of using old queries retrieving on a different old collection, were not official because of late submission. Stage-2 submissions, which consists of repeating previous experiments, were on time. These NTCIR-6 experiments were conducted as new without referring to any previous knowledge about the runs. Comparisons with old results however were less favorable for about half the runs. We traced this to the accidental use of an out-dated module which sets the Zipf high frequency threshold too low, and leads to too many high frequency terms being removed from a query. Some runs are new and not submitted previously by us. These include: ‘title’ queries for NTCIR-3 monolingual Chinese and English-Chinese CLIR, and the English-Chinese CLIR runs for