Re: [R] Nolinear mixed-effects models (nlme)

From: Douglas Bates <dmbates_at_gmail.com>
Date: Fri 01 Jul 2005 - 23:46:35 EST

On 6/30/05, Alex Bach <alex.bach@irta.es> wrote:
> Hello,
>
> I am trying to fit a nonlinear model of the form of:
>
> A*x^b*exp(-c*x)
>
> This represents a lactation curve. I have a bunch of cows, so I want
> COW to be a random effect.

You need to decide which of the model parameters (i.e. A, B and C) should have a random effect grouped by COW and to specify this in your call to nlme.

>
> I have been trying the following code with very littel success:
>
> > fm1 <- nlme(yield ~ A*(DIM^B)*(exp(-C*DIM)),
> + data = group,
> + fixed = A + B + C ~ 1,
> + start = c(A = 20, B = 0.3, C = 0.03))
>
> Does anyone know how to add the random effect of the cow? I have used
> the command groupedData to have Cow as subject (i.e., yield~DIM |
> cow). Is this a valid and sufficient approach? I have the feeling it
> is not sufficient.
>
> Also, does anyone know whether the formulation of the fixed effects
> is correct?.
>
> Thank you very much,
>
> Alex
>
>
>
> [[alternative HTML version deleted]]
>
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R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Fri Jul 01 23:52:43 2005

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