[R-sig-ME] How to implement nested fixed effect

ONKELINX, Thierry Thierry.ONKELINX at inbo.be
Mon Oct 20 17:33:03 CEST 2008

Dear all,

First let me start with a brief description of the design of the study.
A colleague examined the effect of 6 different products (including one
blanco). Each product was applied in two doses: a base dose and twice
the base dose. The blanco has offcourse only one dose. Each plot was
measured twice after treatment.
What we want to know is: is there a difference between the products, is
there a difference between the doses and is there a difference between
the years.

So what I tried was:
lme(Response ~ Product * Dose * Year, random = ~1|plot)
But I got 
Error in MEEM(object, conLin, control$niterEM) : 
  Singularity in backsolve at level 0, block 1
I noticed that lm(Response ~ Product * Dose * Year) yields two
coefficients with NA: one for Product5:Dose and one for
Product5:Dose:Year2. Hence I suppose the problem is due to single dosage
for the blanc product (=no treatment). Any solutions to solve this. Or
should I better stick to lme(Response ~ Treatment * Year, random =
~1|plot) where Treatment combines the info from Product and Dose.


ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature
and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
tel. + 32 54/436 185
Thierry.Onkelinx at inbo.be 

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