German, French, English and Persian Retrieval Experiments at CLEF 2008

We describe evaluation experiments conducted by submitting retrieval runs for the monolingual German, French, English and Persian (Farsi) information retrieval tasks of the Ad-Hoc Track of the Cross-Language Evaluation Forum (CLEF) 2008. In the ad hoc retrieval tasks, the system was given 50 natural language queries, and the goal was to find all of the relevant records or documents (with high precision) in a par-ticular document set. We conducted diagnostic experiments with different techniques for matching word variations, comparing the performance on the robust Generalized Success@10 measure and the non-robust mean average precision measure. The mea-sures generally agreed on the mean benefits of morphological techniques such as de-compounding and stemming, but generally disagreed on the blind feedback technique, though not all of the mean differences were statistically significant. Also, for each language, we submitted a sample of the first 10000 retrieved items to investigate the frequency of relevant items at deeper ranks than the official judging depth of 60. The results suggest that, on average, the percentage of relevant items assessed was less than 55 % for each of German, French and English and less than 25 % for Persian