QACTIS Enhancements in TREC QA 2006

The QACTIS system has been tested in previous years at the TREC Question Answering Evaluations. This paper describes new enhancements to the system specific to TREC-2006, including basic improvements and threshold- ing experiments, filtered and Internet-supported pseudo-rel- evance feedback for information retrieval, and emerging statistics-driven question-answering. For contrast, we also compare our TREC-2006 system performance to that of our top systems from TREC-2004 and TREC-2005 applied to this year's data. Lastly, we analyze evaluator-declared unsupportedness of factoids and nugget decisions of "other"questions to understand major negative changes in performance for these categories over last year.