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From Sean Owen <sro...@gmail.com>
Subject Re: GLM Poisson Model - Deviance calculations
Date Thu, 19 Apr 2018 13:56:10 GMT
I see, this was handled for binomial deviance by the 'ylogy' method, which
computes y log (y / mu), defining this to be 0 when y = 0. It's not
necessary to add a delta or anything; 0 is the limit as y goes to 0 so it's
fine.

 The same change is appropriate for Poisson deviance. Gamma deviance looks
like it also has this issue but I suppose it isn't defined at 0 anyway. I
don't know if implementations still try to return something that isn't NaN
or what here.

Anyway, I think it's fine to open a JIRA and PR to make that change.

On Wed, Apr 18, 2018 at 9:30 PM svattig <srikar.vattigunta@gmail.com> wrote:

> Yes i’m referring to that method deviance. It fails when ever y is 0. I
> think
> R deviance calculation logic checks if y is 0 and assigns 1 to y for such
> cases.
>
> There are few deviances Like nulldeviance, residualdiviance and deviance
> that Glm regression summary object has.
> You might want to check those as well so the toString method doesn’t fail.
>
> Thank you,
> Srikar.V
>
>
>
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