Okapi at TREC-7: Automatic Ad Hoc, Filtering, VLC and Interactive

Three runs were submitted: medium (title and description), short (title only) and a run which was a combination of a long run (title, description and narrative) with the medium and short runs. The average precision of the last mentioned run was higher by several percent than any other submitted run, but another participant recently noticed an impossibly high score for one topic in the short run. This led to the discovery that due to a mistake in the indexing procedures part of the SUBJECT eld of the LA Times documents had been indexed. Use of this eld was explicitly forbidden in the guidelines [1] for the ad hoc track. The o cial runs were repeated against a corrected index, and the corrected results are reported below, average precisions being reduced by about 2{4%.