[R] fitting growth curves

[Daniel A. Powers]

Antonio --

You can estimate a linear mixed model with lme in library(nlme). Models
typically take a long time to estimate compared to sas proc mixed (but I
had a few thousand observations).  The nonlinear mixed models can be done
using nlme in library(nlme). However, I'm not clear on how to set up the
functions. If someone has a complete example (with function), I'd like to
see it.

Note that SAS now has proc NLMixed (not a macro).

Cheers,
Dan

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Dan Powers
Associate Professor, Sociology
University of Texas at Austin


On Wed, 28 Mar 2001, Antonio Olinto wrote:

> Dear R-list members,
>
> Cynthia M. Jones wrote a paper (Fitting growth curves to retrospective
> size-at-age data, Fisheries Research 46(2000):123-129; abstract at
> http://www.elsevier.nl/gej-ng/10/19/44/70/24/37/abstract.html)where the
> SAS procedure MIXED, Macro NLINMIX (Littell et. al., 1996)was used to
> estimate the von Bertalanffy growth function parameters assuming that
> data from the same fish are repeated-measures with autoregressive
> correlation structure and fitting with a nonlinear repeated-measures
> model.
>
> Is there any similar procedure that I can use in R?
>
> Thanks,
>
> Antonio Olinto
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