[R] Add covariate in nlme?

hwouters heidiwout at gmail.com
Thu Apr 19 10:05:24 CEST 2012

Dear Ben,

Thanks for your useful information. Now I know at least what I do not want

The sas-code that corresponds to what I want is:
proc nlmixed data=stab.BatchdataParameter ;
	parms Ea=92 A0=93 A1=34.5 e=10 s2=10 A11=1 A12=1;
	k= exp(A1)*exp(-Ea/(.0083144*tempK))*exp(eps1)*exp(A11*(Process='Process
1') + A12*(Process='Process 3'));
	m= A0*exp(-k*time);
	model result ~ normal(m,e);
	random eps1~normal(0,s2) subject=batch;

So I defenitely want that A1 varies (fixed) across Processes (like in the
sas-code above, there are three processes). The other attempts were just a
selection of what I was trying to make things work and to understand better
what the function nlme was doing.

I checked the NAs in my data and no NAs are present so the problem might be
something else.

Could it be that I only have One batch for Process 2 and Process 3 while I'm
having five batches for Process 1?
Sas is not having problems with that...

Thanks again for you quick reply.

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