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From Grant Ingersoll <>
Subject Re: Calculating a search engine's MAP
Date Wed, 23 Dec 2009 14:45:02 GMT

On Dec 16, 2009, at 8:26 AM, Ludovico Boratto wrote:

> Hi,
> thanks for your reply.
> How can trec_eval work properly?
> A standard TREC rank contains 1000 results, while the relevants judgments are about a
much smaller amount of documents (usually 50).
> How can I calculate precision and recall if I don't know how relevant are the 95% of
the documents in the ranking I produced?

You calculate them on the amount you have, i.e. precision at 50 (or 10 or whatever).  1000
results is overkill for all practical purposes anyway. 

The formula is pretty straightforward:

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