[Corpora-List] Precision and Recall

[Angus Grieve-Smith]

On Fri, 18 Apr 2008, Adam Funk wrote:

> [18/04/08 08:39] Daniel Zeman wrote:
>
>> Alternative wording I usually tell my students:
>>
>> P = number of things I correctly found / number of things I found
>> R = number of things I correctly found / number of things I should have
>> found
>>
>> ("correctly found" = "I found it" AND "I should have found it")
>
> Here's another way to look at it, which I sometimes find useful:
>
> P = true_positives / (true_positives + false_positives)
>
> R = true_positives / (true_positives + false_negatives)

 	Thank you both for bringing clarity to this topic!  Can anyone 
tell me why precision and recall are more useful than the simple numbers 
of false positives and false negatives?  What do you get out of mixing 
that up with the number of true positives, some kind of odds ratio?

 					-Angus B. Grieve-Smith
 					grvsmth at panix.com

Find out more about my computer consulting service at
<http://www.grieve-smith.com/>.  Discounts are available
for nonprofits and for customers in the Sunnyside/Woodside area.

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