Dear R-users I'm modelling some longitudinal data (1 response variable measured at 6 occasions, 1 baseline, one "treatment" variable) collected in the same subjects using the following model: library(nlme) model.lme <- lme(response ~ V0+ time+ tt + tt:time, random = ~1|subject, correlation = corSymm(form = ~ 1 | subject), na.action=na.omit, data=arm.total2) Then I would lke to estimate the effect of "treatment" at time = 6 using the package "contrast" library(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. Jacques -- View this message in context: http://old.nabble.com/contrast-in-lme-tp26281409p26281409.html Sent from the R help mailing list archive at Nabble.com.