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From Sean Owen <sro...@gmail.com>
Subject Re: Two learning competitions that might be of interest for Mahout
Date Tue, 15 Feb 2011 17:52:49 GMT
Hmm, not sure I understand. No, it's not true that real-life data
regularly omits the user's top ratings. Why would that be?

How would you score the recommendations by holding out a random
subset? That subset is definitely *not* representative of good
recommendations -- you might be picking out things the user hates.

Precision / recall don't really make sense unless you think you're
holding out "good" recommendations and those would have to be top
rated items.

Sean

On Tue, Feb 15, 2011 at 5:36 PM, Chen_1st <y.c@live.cn> wrote:
> Hi, Sean,
>
> I cannot agree with you.
>
> The small problem you mentioned might incur difficulties in prediction
> indeed, but such problem also occurs in real life applications, right?
>
> As to the big problem you mentioned,  of course, we don't have the complete
> set of true result, but if the available subset of true result is randomly
> selected from the complete set, I think the evaluation criteria like
> recall@k, precision@k, or ndcg are still meaningful.
>
>

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