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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 16:40:52 -0400

That's a good idea. Fortunately for me, there is no one with a 1.0 in
any of the hormones at any of the three time points.

On 10/8/07, Nick Cox <n.j.cox@durham.ac.uk> wrote:
> 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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