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From Grant Ingersoll <gsing...@apache.org>
Subject Re: compare scores across queries
Date Thu, 20 Nov 2008 13:22:32 GMT
No, they should not be compared.  Scores are only relative to each  
other for that given input query, despite what the queryNorm docs  
say.  The queryNorm was an attempt at doing it, but my understanding  
of the research still indicates they are not comparable.

-Grant

On Nov 18, 2008, at 12:02 PM, Ng Vinny wrote:

> Hi all,
>
> I am wondering if the raw scores obtained from HitCollector can be  
> used to
> compare relevance of documents to different queries?
>
> E.g.  two  phrase queries are issued : (PQ1: "Barack Obama"  and  
> PQ2:  "John
> McCain"). if a document (doc1) belongs to the result sets of both  
> queries
> and has the raw score of 5 for PQ1 and 3 for PQ2, can  I say that  
> doc1 is
> more relevant to "Barack Obama" than to "John McCain"?
>
> There have been some previous discussions about this at [1,2]. On  
> the other
> hand, the javadoc of the Similarity class says "*queryNorm(q) * is a
> normalizing factor used to make scores between queries comparable.  
> This
> factor does not affect document ranking (since all ranked documents  
> are
> multiplied by the same factor), but rather just attempts to make  
> scores from
> different queries (or even different indexes) comparable. "
>
> Please advise.
>
> Thanks.
> Ng.
>
> [1] http://thread.gmane.org/gmane.comp.jakarta.lucene.user/10760/focus=10810
> [2]
> http://www.gossamer-threads.com/lists/lucene/java-user/35051?search_string=compare%20score%20across%20queries;#35051
> [3]
> http://hudson.zones.apache.org/hudson/job/Lucene-trunk/javadoc//org/apache/lucene/search/Similarity.html

--------------------------
Grant Ingersoll

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