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Re: st: RE: GLLAMM error: log-likelihood cannot be computed


From   "Leny Mathew" <lenymathewc@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: GLLAMM error: log-likelihood cannot be computed
Date   Mon, 8 Oct 2007 15:58:39 -0400

Thanks Nick. For the purposes of the graph, I created a new variable
with the zeros changed to 1 and then took the log; effectively setting
them as zero in the log graph. I guess I could scale the variable by a
 very small value and then take the log also.

On 10/8/07, Nick Cox <n.j.cox@durham.ac.uk> wrote:
> -gllamm- I leave to experts on it.
>
> -glm- produces predictions on the scale of the response,
> whatever the link. It can also be quite sensible to use a
> log scale for subsequent graphing. Indeed I've found
> log link and log scale for graphs invaluable in some cases.
> The results are not equivalent to transforming the response
> because the log of the mean is not in general the mean
> of the logs (and similarly for any nonlinear transformation).
>
> However, you can't show zeros on a log scale. If you
> try this, Stata just gives you a dopey graph. That's
> its way of saying "Isn't that rather a silly thing
> to ask for?"
>
> Nick
> n.j.cox@durham.ac.uk
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