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

["Airey, David C" <david.airey@vanderbilt.edu>]

.

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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