RE: [R] lme model specification

From: Eric Hack <hack_at_tera.org>
Date: Fri 10 Jun 2005 - 04:28:30 EST


Thanks for the response. It is actually a repeated measures study, I just mention the fixed effects specification because I think I know the random effect specification, i.e.:
Random = ~ 1|subject

And thanks for the tip about the nonlinear model and the S-plus list. I will check out nlme and the other list.

Eric

On 6/9/05, Eric Hack <hack@tera.org> wrote:
> Dear All,
>
>
>
> I am trying to specify the following fixed effects model for lme:

If you have a linear fixed-effects model you should use lm, not lme.

>
> y ~ constant1 - beta1*(x - beta2)
>
> where y is the response, x is the independent variable, and the
> operators above are real arithmetic operations of addition,
subtraction,
> and multiplication. I realize that this model is just a
> reparameterization of y=beta0+beta1*x, but I am using this
> parameterization because I am specifically interested in confidence
> bounds for beta2.

You would need to fit that as a nonlinear model. In reference to such models "linear" means "linear in the parameters" and that model isn't.  

> I have looked at the help, but the closest hint I find is the I()
> function, and that does not seem to work this way.
>
>
>
> I confess that I am actually using S-plus, but there does not seem to
be
> a resource like this list for S-plus.

Look for the S-news email list (http://www.biostat.wustl.edu/s-news/)



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