[R-sig-ME] syntax for indicating fixed covariates in nlmer ?

Laurent Gentzbittel gentz at ensat.fr
Tue Mar 10 16:56:56 CET 2009

Dear all,

I would like to use the nlmer for fitting logistic curves to disease
index curves. I'm typically comparing different plant lines (several
plants from each line are subjected to a pathogen) and would like to
test if the 'population' (fixed effects) parameters of the curves are
the same between the lines.
I need to specify a random effect for each parameter to account for
plant-to-plant variability and a fixed effect for some parameter to
account for 'general' differences among lines.
I previously used the nlme function of the nlme package and was able to
specify both fixed and random effects for each parameter, including a
fixed covariate 'line' for example.

I would like to switch to the lme4 package, but I was unable to find how
to specify fixed covariates (fixed effects) in the formula.
A search in the different mail lists and Googl'ing  was also unsuccessful.

Does anybody knows how to write it ?


Prof. L. GENTZBITTEL            Phone: +33 (0)5 62 19 35 96
INP - ENSAT                     Fax  : +33 (0)5 62 19 35 89
Symb. & Path. Plantes   - IFR40
18, Chemin de Borde Rouge - Auzeville Tolosane
E-mail:                         gentz at ensat.fr
Plant genomes synteny  :       
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