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


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: RE: GLLAMM error: log-likelihood cannot be computed
Date   Mon, 8 Oct 2007 21:09:23 +0100

So, a log of 0 sometimes means that the data are 1 
and sometimes that they are 0? 

There's no neat solution to this one. 

Nick 
n.j.cox@durham.ac.uk 

Leny Mathew
 
> 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?"

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