[R-sig-ME] Contrasts with nlme

Jacques Ropers jropers at gmail.com
Tue Nov 10 21:11:41 CET 2009

Dear All,

I'm modelling some longitudinal data (1 continuous
response variable measured at 6 times (covariate time taken as factor), 
1 continuous baseline, one "treatment" variable also taken as a factor) 
collected in the same subjects using the following model:

model.lme<- lme(response ~ V0+ time + tt + tt:time, random = 
~1|subject,correlation = corSymm(form = ~ 1 | subject), 
na.action=na.omit, data=total)

Then I would lke to estimate the effect of "treatment" at time = 6 using 
the package "contrast"

contrast(model.lme ,
a = list(tt="1",time="6"),
b = list(tt="0",time="6")

But I get the following error message
"Erreur dans gendata.default(fit = list(modelStruct = list(reStruct = 
list(:   not enough factors"

I'm obviously doing something wrong.

Thanks for your help.


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