[R] extension to nlme self start SSmicmen?

[David Airey]

> Dear list,
>
> Has anyone created a version of SSmicmen that allows testing for  
> group differences? The basic Michaelis-Menten equation is:
>
> (Bmax * X) / (Kd + X).
>
> The nlme package allows modeling of random effects for Bmax and Kd  
> as needed, but I curious how I can build in group differences? I  
> have receptor binding data for strains of mice, and following  
> Pinheiro and Bates' lead in their book, a random effort for animal  
> differences in Bmax seems reasonable, within strain. However, I'd  
> like a self-start function, or even just the equation above,  
> modified to allow testing for strain differences in Bmax and or Kd.
>
> Thank you.
>
> -Dave

Reading more closely, I now think I don't have to change the self  
start function SSmicmen to test for treatment group fixed effects. I  
just need to get the list of fixed effects right, to include the  
strain factor. Something like "fixed = list(bmax + kd ~ strain),  
random = list(bmax + kd ~ 1)".