Re: st: non-linear regression with mixed cross-sectional and longitudinal data

[Kirstie Whitaker <kirstie.whitaker@berkeley.edu>]

Oh my goodness - I'm terribly sorry for the silly question then -
thank you for pointing that out to me!

Kx

On Thu, Jun 21, 2012 at 9:36 PM, Airey, David C
<david.airey@vanderbilt.edu> wrote:
>
> .
>
> In looking at the nl command in Stata, it does allow vce(cluster clustvar) option.
>
> -Dave
>
> > For nonlinear mixed effect models your probably have to look to using different
> > software, like SAS NLMIXED, R nlme, or ADMB (http://admb-project.org/).
> >
> > I'd be interested in hearing about solutions in Stata too.
> >
> > Interesting work.
> >
> > -Dave
>
> > Hi Stata-list,
> >
> > I'm a long time listener, first time caller.  Thank you for all the
> > help you've provided over the years.
> >
> > I'm calculating regression models of the form
> >
> > y = a + b * exp( -x / c)
> >
> > (where a, b and c are the parameters I'm looking to estimate)
> >
> > with the command:
> >
> > nl ( WMI = {alpha} + {beta}*exp(-Age/{time=1}) )
> >
> > (If you're interested - this is looking at the developmental
> > trajectory of white matter in the adolescent brain)
> >
> > My data set has some participants who have been in for two scans,
> > about 18 months apart.  I'd like to be able to include all the data in
> > my model, using for example xtmixed with a random effect of subjectID
> > or regress with the cluster(subID) option however I'm not sure how to
> > fit the hypothesized model (see above) into either of these
> > frameworks, or if I can use nl with a random effect.
> >
> > Does anyone have an idea?  I wonder if there is a way to model this in
> > a linear way that I'm just not seeing?
> >
> > Thank you for all the help!
> > Kx
> >
>
>
>
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-----------------------
Kirstie Whitaker
Doctoral Candidate
Bunge Laboratory: Building Blocks of Cognition
Helen Wills Neuroscience Institute
University of California at Berkeley
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