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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 21:33:31 +0100

But I think the least unsatisfactory options 
are 

1. To omit zeros and to indicate them by a rug of ticks 
on the other axis. 

2. To plot downward-pointing arrows at say 
log(0.5). Whatever constant is used should 
be less than the smallest positive value observed. 

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

> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu]On Behalf Of Nick Cox
> Sent: 08 October 2007 21:09
> To: statalist@hsphsun2.harvard.edu
> Subject: RE: st: RE: GLLAMM error: log-likelihood cannot be computed
> 
> 
> 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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