Generally, the performance of IR system can be determined by 2 factors, precision and recall, which may play different roles in different cases. Most of time, when the user hope to get much more relevent information ranked high in a quite short time, then he/she hope IR system to be more precise. while sometimes, when users wish to get more relevant information even if it has a little bit relationship with the key words, in this situation, he/she needs "recall".
But as to the design of IR system, we'd better make the trade off between them.
Shu Wang
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Best wishes,
Shu Wang
Computer Science Department
Arizona State University
Arizona State University
